diff --git a/literal/Cargo.toml b/literal/Cargo.toml
index 7afa9db..c5b8925 100644
--- a/literal/Cargo.toml
+++ b/literal/Cargo.toml
@@ -8,8 +8,10 @@ repository = "https://github.com/RustPython/RustPython"
 license = "MIT"
 
 [dependencies]
+bitflags = "2.2.1"
+itertools = "0.10.5"
+num-bigint = { workspace = true }
 num-traits = { workspace = true }
-
 hexf-parse = "0.2.1"
 lexical-parse-float = { version = "0.8.0", features = ["format"] }
 unic-ucd-category = "0.9"
diff --git a/literal/src/cformat.rs b/literal/src/cformat.rs
new file mode 100644
index 0000000..4be669a
--- /dev/null
+++ b/literal/src/cformat.rs
@@ -0,0 +1,1044 @@
+//! Implementation of Printf-Style string formatting
+//! as per the [Python Docs](https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting).
+use crate::{float, format::Case};
+use bitflags::bitflags;
+use num_bigint::{BigInt, Sign};
+use num_traits::Signed;
+use std::{
+    cmp, fmt,
+    iter::{Enumerate, Peekable},
+    str::FromStr,
+};
+
+#[derive(Debug, PartialEq)]
+pub enum CFormatErrorType {
+    UnmatchedKeyParentheses,
+    MissingModuloSign,
+    UnsupportedFormatChar(char),
+    IncompleteFormat,
+    IntTooBig,
+    // Unimplemented,
+}
+
+// also contains how many chars the parsing function consumed
+pub type ParsingError = (CFormatErrorType, usize);
+
+#[derive(Debug, PartialEq)]
+pub struct CFormatError {
+    pub typ: CFormatErrorType, // FIXME
+    pub index: usize,
+}
+
+impl fmt::Display for CFormatError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use CFormatErrorType::*;
+        match self.typ {
+            UnmatchedKeyParentheses => write!(f, "incomplete format key"),
+            IncompleteFormat => write!(f, "incomplete format"),
+            UnsupportedFormatChar(c) => write!(
+                f,
+                "unsupported format character '{}' ({:#x}) at index {}",
+                c, c as u32, self.index
+            ),
+            IntTooBig => write!(f, "width/precision too big"),
+            _ => write!(f, "unexpected error parsing format string"),
+        }
+    }
+}
+
+pub type CFormatConversion = super::format::FormatConversion;
+
+#[derive(Debug, PartialEq)]
+pub enum CNumberType {
+    Decimal,
+    Octal,
+    Hex(Case),
+}
+
+#[derive(Debug, PartialEq)]
+pub enum CFloatType {
+    Exponent(Case),
+    PointDecimal(Case),
+    General(Case),
+}
+
+#[derive(Debug, PartialEq)]
+pub enum CFormatType {
+    Number(CNumberType),
+    Float(CFloatType),
+    Character,
+    String(CFormatConversion),
+}
+
+#[derive(Debug, PartialEq)]
+pub enum CFormatPrecision {
+    Quantity(CFormatQuantity),
+    Dot,
+}
+
+impl From<CFormatQuantity> for CFormatPrecision {
+    fn from(quantity: CFormatQuantity) -> Self {
+        CFormatPrecision::Quantity(quantity)
+    }
+}
+
+bitflags! {
+    #[derive(Copy, Clone, Debug, PartialEq)]
+    pub struct CConversionFlags: u32 {
+        const ALTERNATE_FORM = 0b0000_0001;
+        const ZERO_PAD = 0b0000_0010;
+        const LEFT_ADJUST = 0b0000_0100;
+        const BLANK_SIGN = 0b0000_1000;
+        const SIGN_CHAR = 0b0001_0000;
+    }
+}
+
+impl CConversionFlags {
+    #[inline]
+    pub fn sign_string(&self) -> &'static str {
+        if self.contains(CConversionFlags::SIGN_CHAR) {
+            "+"
+        } else if self.contains(CConversionFlags::BLANK_SIGN) {
+            " "
+        } else {
+            ""
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum CFormatQuantity {
+    Amount(usize),
+    FromValuesTuple,
+}
+
+#[derive(Debug, PartialEq)]
+pub struct CFormatSpec {
+    pub mapping_key: Option<String>,
+    pub flags: CConversionFlags,
+    pub min_field_width: Option<CFormatQuantity>,
+    pub precision: Option<CFormatPrecision>,
+    pub format_type: CFormatType,
+    pub format_char: char,
+    // chars_consumed: usize,
+}
+
+impl FromStr for CFormatSpec {
+    type Err = ParsingError;
+
+    fn from_str(text: &str) -> Result<Self, Self::Err> {
+        let mut chars = text.chars().enumerate().peekable();
+        if chars.next().map(|x| x.1) != Some('%') {
+            return Err((CFormatErrorType::MissingModuloSign, 1));
+        }
+
+        CFormatSpec::parse(&mut chars)
+    }
+}
+
+pub type ParseIter<I> = Peekable<Enumerate<I>>;
+
+impl CFormatSpec {
+    pub fn parse<T, I>(iter: &mut ParseIter<I>) -> Result<Self, ParsingError>
+    where
+        T: Into<char> + Copy,
+        I: Iterator<Item = T>,
+    {
+        let mapping_key = parse_spec_mapping_key(iter)?;
+        let flags = parse_flags(iter);
+        let min_field_width = parse_quantity(iter)?;
+        let precision = parse_precision(iter)?;
+        consume_length(iter);
+        let (format_type, format_char) = parse_format_type(iter)?;
+
+        Ok(CFormatSpec {
+            mapping_key,
+            flags,
+            min_field_width,
+            precision,
+            format_type,
+            format_char,
+        })
+    }
+
+    fn compute_fill_string(fill_char: char, fill_chars_needed: usize) -> String {
+        (0..fill_chars_needed)
+            .map(|_| fill_char)
+            .collect::<String>()
+    }
+
+    fn fill_string(
+        &self,
+        string: String,
+        fill_char: char,
+        num_prefix_chars: Option<usize>,
+    ) -> String {
+        let mut num_chars = string.chars().count();
+        if let Some(num_prefix_chars) = num_prefix_chars {
+            num_chars += num_prefix_chars;
+        }
+        let num_chars = num_chars;
+
+        let width = match &self.min_field_width {
+            Some(CFormatQuantity::Amount(width)) => cmp::max(width, &num_chars),
+            _ => &num_chars,
+        };
+        let fill_chars_needed = width.saturating_sub(num_chars);
+        let fill_string = CFormatSpec::compute_fill_string(fill_char, fill_chars_needed);
+
+        if !fill_string.is_empty() {
+            if self.flags.contains(CConversionFlags::LEFT_ADJUST) {
+                format!("{string}{fill_string}")
+            } else {
+                format!("{fill_string}{string}")
+            }
+        } else {
+            string
+        }
+    }
+
+    fn fill_string_with_precision(&self, string: String, fill_char: char) -> String {
+        let num_chars = string.chars().count();
+
+        let width = match &self.precision {
+            Some(CFormatPrecision::Quantity(CFormatQuantity::Amount(width))) => {
+                cmp::max(width, &num_chars)
+            }
+            _ => &num_chars,
+        };
+        let fill_chars_needed = width.saturating_sub(num_chars);
+        let fill_string = CFormatSpec::compute_fill_string(fill_char, fill_chars_needed);
+
+        if !fill_string.is_empty() {
+            // Don't left-adjust if precision-filling: that will always be prepending 0s to %d
+            // arguments, the LEFT_ADJUST flag will be used by a later call to fill_string with
+            // the 0-filled string as the string param.
+            format!("{fill_string}{string}")
+        } else {
+            string
+        }
+    }
+
+    fn format_string_with_precision(
+        &self,
+        string: String,
+        precision: Option<&CFormatPrecision>,
+    ) -> String {
+        // truncate if needed
+        let string = match precision {
+            Some(CFormatPrecision::Quantity(CFormatQuantity::Amount(precision)))
+                if string.chars().count() > *precision =>
+            {
+                string.chars().take(*precision).collect::<String>()
+            }
+            Some(CFormatPrecision::Dot) => {
+                // truncate to 0
+                String::new()
+            }
+            _ => string,
+        };
+        self.fill_string(string, ' ', None)
+    }
+
+    #[inline]
+    pub fn format_string(&self, string: String) -> String {
+        self.format_string_with_precision(string, self.precision.as_ref())
+    }
+
+    #[inline]
+    pub fn format_char(&self, ch: char) -> String {
+        self.format_string_with_precision(
+            ch.to_string(),
+            Some(&(CFormatQuantity::Amount(1).into())),
+        )
+    }
+
+    pub fn format_bytes(&self, bytes: &[u8]) -> Vec<u8> {
+        let bytes = if let Some(CFormatPrecision::Quantity(CFormatQuantity::Amount(precision))) =
+            self.precision
+        {
+            &bytes[..cmp::min(bytes.len(), precision)]
+        } else {
+            bytes
+        };
+        if let Some(CFormatQuantity::Amount(width)) = self.min_field_width {
+            let fill = cmp::max(0, width - bytes.len());
+            let mut v = Vec::with_capacity(bytes.len() + fill);
+            if self.flags.contains(CConversionFlags::LEFT_ADJUST) {
+                v.extend_from_slice(bytes);
+                v.append(&mut vec![b' '; fill]);
+            } else {
+                v.append(&mut vec![b' '; fill]);
+                v.extend_from_slice(bytes);
+            }
+            v
+        } else {
+            bytes.to_vec()
+        }
+    }
+
+    pub fn format_number(&self, num: &BigInt) -> String {
+        use CNumberType::*;
+        let magnitude = num.abs();
+        let prefix = if self.flags.contains(CConversionFlags::ALTERNATE_FORM) {
+            match self.format_type {
+                CFormatType::Number(Octal) => "0o",
+                CFormatType::Number(Hex(Case::Lower)) => "0x",
+                CFormatType::Number(Hex(Case::Upper)) => "0X",
+                _ => "",
+            }
+        } else {
+            ""
+        };
+
+        let magnitude_string: String = match self.format_type {
+            CFormatType::Number(Decimal) => magnitude.to_str_radix(10),
+            CFormatType::Number(Octal) => magnitude.to_str_radix(8),
+            CFormatType::Number(Hex(Case::Lower)) => magnitude.to_str_radix(16),
+            CFormatType::Number(Hex(Case::Upper)) => {
+                let mut result = magnitude.to_str_radix(16);
+                result.make_ascii_uppercase();
+                result
+            }
+            _ => unreachable!(), // Should not happen because caller has to make sure that this is a number
+        };
+
+        let sign_string = match num.sign() {
+            Sign::Minus => "-",
+            _ => self.flags.sign_string(),
+        };
+
+        let padded_magnitude_string = self.fill_string_with_precision(magnitude_string, '0');
+
+        if self.flags.contains(CConversionFlags::ZERO_PAD) {
+            let fill_char = if !self.flags.contains(CConversionFlags::LEFT_ADJUST) {
+                '0'
+            } else {
+                ' ' // '-' overrides the '0' conversion if both are given
+            };
+            let signed_prefix = format!("{sign_string}{prefix}");
+            format!(
+                "{}{}",
+                signed_prefix,
+                self.fill_string(
+                    padded_magnitude_string,
+                    fill_char,
+                    Some(signed_prefix.chars().count()),
+                ),
+            )
+        } else {
+            self.fill_string(
+                format!("{sign_string}{prefix}{padded_magnitude_string}"),
+                ' ',
+                None,
+            )
+        }
+    }
+
+    pub fn format_float(&self, num: f64) -> String {
+        let sign_string = if num.is_sign_negative() && !num.is_nan() {
+            "-"
+        } else {
+            self.flags.sign_string()
+        };
+
+        let precision = match &self.precision {
+            Some(CFormatPrecision::Quantity(quantity)) => match quantity {
+                CFormatQuantity::Amount(amount) => *amount,
+                CFormatQuantity::FromValuesTuple => 6,
+            },
+            Some(CFormatPrecision::Dot) => 0,
+            None => 6,
+        };
+
+        let magnitude_string = match &self.format_type {
+            CFormatType::Float(CFloatType::PointDecimal(case)) => {
+                let magnitude = num.abs();
+                float::format_fixed(
+                    precision,
+                    magnitude,
+                    *case,
+                    self.flags.contains(CConversionFlags::ALTERNATE_FORM),
+                )
+            }
+            CFormatType::Float(CFloatType::Exponent(case)) => {
+                let magnitude = num.abs();
+                float::format_exponent(
+                    precision,
+                    magnitude,
+                    *case,
+                    self.flags.contains(CConversionFlags::ALTERNATE_FORM),
+                )
+            }
+            CFormatType::Float(CFloatType::General(case)) => {
+                let precision = if precision == 0 { 1 } else { precision };
+                let magnitude = num.abs();
+                float::format_general(
+                    precision,
+                    magnitude,
+                    *case,
+                    self.flags.contains(CConversionFlags::ALTERNATE_FORM),
+                    false,
+                )
+            }
+            _ => unreachable!(),
+        };
+
+        if self.flags.contains(CConversionFlags::ZERO_PAD) {
+            let fill_char = if !self.flags.contains(CConversionFlags::LEFT_ADJUST) {
+                '0'
+            } else {
+                ' '
+            };
+            format!(
+                "{}{}",
+                sign_string,
+                self.fill_string(
+                    magnitude_string,
+                    fill_char,
+                    Some(sign_string.chars().count()),
+                )
+            )
+        } else {
+            self.fill_string(format!("{sign_string}{magnitude_string}"), ' ', None)
+        }
+    }
+}
+
+fn parse_spec_mapping_key<T, I>(iter: &mut ParseIter<I>) -> Result<Option<String>, ParsingError>
+where
+    T: Into<char> + Copy,
+    I: Iterator<Item = T>,
+{
+    if let Some(&(index, c)) = iter.peek() {
+        if c.into() == '(' {
+            iter.next().unwrap();
+            return match parse_text_inside_parentheses(iter) {
+                Some(key) => Ok(Some(key)),
+                None => Err((CFormatErrorType::UnmatchedKeyParentheses, index)),
+            };
+        }
+    }
+    Ok(None)
+}
+
+fn parse_flags<T, I>(iter: &mut ParseIter<I>) -> CConversionFlags
+where
+    T: Into<char> + Copy,
+    I: Iterator<Item = T>,
+{
+    let mut flags = CConversionFlags::empty();
+    while let Some(&(_, c)) = iter.peek() {
+        let flag = match c.into() {
+            '#' => CConversionFlags::ALTERNATE_FORM,
+            '0' => CConversionFlags::ZERO_PAD,
+            '-' => CConversionFlags::LEFT_ADJUST,
+            ' ' => CConversionFlags::BLANK_SIGN,
+            '+' => CConversionFlags::SIGN_CHAR,
+            _ => break,
+        };
+        iter.next().unwrap();
+        flags |= flag;
+    }
+    flags
+}
+
+fn consume_length<T, I>(iter: &mut ParseIter<I>)
+where
+    T: Into<char> + Copy,
+    I: Iterator<Item = T>,
+{
+    if let Some(&(_, c)) = iter.peek() {
+        let c = c.into();
+        if c == 'h' || c == 'l' || c == 'L' {
+            iter.next().unwrap();
+        }
+    }
+}
+
+fn parse_format_type<T, I>(iter: &mut ParseIter<I>) -> Result<(CFormatType, char), ParsingError>
+where
+    T: Into<char>,
+    I: Iterator<Item = T>,
+{
+    use CFloatType::*;
+    use CNumberType::*;
+    let (index, c) = match iter.next() {
+        Some((index, c)) => (index, c.into()),
+        None => {
+            return Err((
+                CFormatErrorType::IncompleteFormat,
+                iter.peek().map(|x| x.0).unwrap_or(0),
+            ));
+        }
+    };
+    let format_type = match c {
+        'd' | 'i' | 'u' => CFormatType::Number(Decimal),
+        'o' => CFormatType::Number(Octal),
+        'x' => CFormatType::Number(Hex(Case::Lower)),
+        'X' => CFormatType::Number(Hex(Case::Upper)),
+        'e' => CFormatType::Float(Exponent(Case::Lower)),
+        'E' => CFormatType::Float(Exponent(Case::Upper)),
+        'f' => CFormatType::Float(PointDecimal(Case::Lower)),
+        'F' => CFormatType::Float(PointDecimal(Case::Upper)),
+        'g' => CFormatType::Float(General(Case::Lower)),
+        'G' => CFormatType::Float(General(Case::Upper)),
+        'c' => CFormatType::Character,
+        'r' => CFormatType::String(CFormatConversion::Repr),
+        's' => CFormatType::String(CFormatConversion::Str),
+        'b' => CFormatType::String(CFormatConversion::Bytes),
+        'a' => CFormatType::String(CFormatConversion::Ascii),
+        _ => return Err((CFormatErrorType::UnsupportedFormatChar(c), index)),
+    };
+    Ok((format_type, c))
+}
+
+fn parse_quantity<T, I>(iter: &mut ParseIter<I>) -> Result<Option<CFormatQuantity>, ParsingError>
+where
+    T: Into<char> + Copy,
+    I: Iterator<Item = T>,
+{
+    if let Some(&(_, c)) = iter.peek() {
+        let c: char = c.into();
+        if c == '*' {
+            iter.next().unwrap();
+            return Ok(Some(CFormatQuantity::FromValuesTuple));
+        }
+        if let Some(i) = c.to_digit(10) {
+            let mut num = i as i32;
+            iter.next().unwrap();
+            while let Some(&(index, c)) = iter.peek() {
+                if let Some(i) = c.into().to_digit(10) {
+                    num = num
+                        .checked_mul(10)
+                        .and_then(|num| num.checked_add(i as i32))
+                        .ok_or((CFormatErrorType::IntTooBig, index))?;
+                    iter.next().unwrap();
+                } else {
+                    break;
+                }
+            }
+            return Ok(Some(CFormatQuantity::Amount(num.unsigned_abs() as usize)));
+        }
+    }
+    Ok(None)
+}
+
+fn parse_precision<T, I>(iter: &mut ParseIter<I>) -> Result<Option<CFormatPrecision>, ParsingError>
+where
+    T: Into<char> + Copy,
+    I: Iterator<Item = T>,
+{
+    if let Some(&(_, c)) = iter.peek() {
+        if c.into() == '.' {
+            iter.next().unwrap();
+            let quantity = parse_quantity(iter)?;
+            let precision = quantity.map_or(CFormatPrecision::Dot, CFormatPrecision::Quantity);
+            return Ok(Some(precision));
+        }
+    }
+    Ok(None)
+}
+
+fn parse_text_inside_parentheses<T, I>(iter: &mut ParseIter<I>) -> Option<String>
+where
+    T: Into<char>,
+    I: Iterator<Item = T>,
+{
+    let mut counter: i32 = 1;
+    let mut contained_text = String::new();
+    loop {
+        let (_, c) = iter.next()?;
+        let c = c.into();
+        match c {
+            _ if c == '(' => {
+                counter += 1;
+            }
+            _ if c == ')' => {
+                counter -= 1;
+            }
+            _ => (),
+        }
+
+        if counter > 0 {
+            contained_text.push(c);
+        } else {
+            break;
+        }
+    }
+
+    Some(contained_text)
+}
+
+#[derive(Debug, PartialEq)]
+pub enum CFormatPart<T> {
+    Literal(T),
+    Spec(CFormatSpec),
+}
+
+impl<T> CFormatPart<T> {
+    #[inline]
+    pub fn is_specifier(&self) -> bool {
+        matches!(self, CFormatPart::Spec(_))
+    }
+
+    #[inline]
+    pub fn has_key(&self) -> bool {
+        match self {
+            CFormatPart::Spec(s) => s.mapping_key.is_some(),
+            _ => false,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct CFormatStrOrBytes<S> {
+    parts: Vec<(usize, CFormatPart<S>)>,
+}
+
+impl<S> CFormatStrOrBytes<S> {
+    pub fn check_specifiers(&self) -> Option<(usize, bool)> {
+        let mut count = 0;
+        let mut mapping_required = false;
+        for (_, part) in &self.parts {
+            if part.is_specifier() {
+                let has_key = part.has_key();
+                if count == 0 {
+                    mapping_required = has_key;
+                } else if mapping_required != has_key {
+                    return None;
+                }
+                count += 1;
+            }
+        }
+        Some((count, mapping_required))
+    }
+
+    #[inline]
+    pub fn iter(&self) -> impl Iterator<Item = &(usize, CFormatPart<S>)> {
+        self.parts.iter()
+    }
+
+    #[inline]
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut (usize, CFormatPart<S>)> {
+        self.parts.iter_mut()
+    }
+}
+
+pub type CFormatBytes = CFormatStrOrBytes<Vec<u8>>;
+
+impl CFormatBytes {
+    pub fn parse<I: Iterator<Item = u8>>(iter: &mut ParseIter<I>) -> Result<Self, CFormatError> {
+        let mut parts = vec![];
+        let mut literal = vec![];
+        let mut part_index = 0;
+        while let Some((index, c)) = iter.next() {
+            if c == b'%' {
+                if let Some(&(_, second)) = iter.peek() {
+                    if second == b'%' {
+                        iter.next().unwrap();
+                        literal.push(b'%');
+                        continue;
+                    } else {
+                        if !literal.is_empty() {
+                            parts.push((
+                                part_index,
+                                CFormatPart::Literal(std::mem::take(&mut literal)),
+                            ));
+                        }
+                        let spec = CFormatSpec::parse(iter).map_err(|err| CFormatError {
+                            typ: err.0,
+                            index: err.1,
+                        })?;
+                        parts.push((index, CFormatPart::Spec(spec)));
+                        if let Some(&(index, _)) = iter.peek() {
+                            part_index = index;
+                        }
+                    }
+                } else {
+                    return Err(CFormatError {
+                        typ: CFormatErrorType::IncompleteFormat,
+                        index: index + 1,
+                    });
+                }
+            } else {
+                literal.push(c);
+            }
+        }
+        if !literal.is_empty() {
+            parts.push((part_index, CFormatPart::Literal(literal)));
+        }
+        Ok(Self { parts })
+    }
+
+    pub fn parse_from_bytes(bytes: &[u8]) -> Result<Self, CFormatError> {
+        let mut iter = bytes.iter().cloned().enumerate().peekable();
+        Self::parse(&mut iter)
+    }
+}
+
+pub type CFormatString = CFormatStrOrBytes<String>;
+
+impl FromStr for CFormatString {
+    type Err = CFormatError;
+
+    fn from_str(text: &str) -> Result<Self, Self::Err> {
+        let mut iter = text.chars().enumerate().peekable();
+        Self::parse(&mut iter)
+    }
+}
+
+impl CFormatString {
+    pub(crate) fn parse<I: Iterator<Item = char>>(
+        iter: &mut ParseIter<I>,
+    ) -> Result<Self, CFormatError> {
+        let mut parts = vec![];
+        let mut literal = String::new();
+        let mut part_index = 0;
+        while let Some((index, c)) = iter.next() {
+            if c == '%' {
+                if let Some(&(_, second)) = iter.peek() {
+                    if second == '%' {
+                        iter.next().unwrap();
+                        literal.push('%');
+                        continue;
+                    } else {
+                        if !literal.is_empty() {
+                            parts.push((
+                                part_index,
+                                CFormatPart::Literal(std::mem::take(&mut literal)),
+                            ));
+                        }
+                        let spec = CFormatSpec::parse(iter).map_err(|err| CFormatError {
+                            typ: err.0,
+                            index: err.1,
+                        })?;
+                        parts.push((index, CFormatPart::Spec(spec)));
+                        if let Some(&(index, _)) = iter.peek() {
+                            part_index = index;
+                        }
+                    }
+                } else {
+                    return Err(CFormatError {
+                        typ: CFormatErrorType::IncompleteFormat,
+                        index: index + 1,
+                    });
+                }
+            } else {
+                literal.push(c);
+            }
+        }
+        if !literal.is_empty() {
+            parts.push((part_index, CFormatPart::Literal(literal)));
+        }
+        Ok(Self { parts })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_fill_and_align() {
+        assert_eq!(
+            "%10s"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_string("test".to_owned()),
+            "      test".to_owned()
+        );
+        assert_eq!(
+            "%-10s"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_string("test".to_owned()),
+            "test      ".to_owned()
+        );
+        assert_eq!(
+            "%#10x"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(0x1337)),
+            "    0x1337".to_owned()
+        );
+        assert_eq!(
+            "%-#10x"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(0x1337)),
+            "0x1337    ".to_owned()
+        );
+    }
+
+    #[test]
+    fn test_parse_key() {
+        let expected = Ok(CFormatSpec {
+            mapping_key: Some("amount".to_owned()),
+            format_type: CFormatType::Number(CNumberType::Decimal),
+            format_char: 'd',
+            min_field_width: None,
+            precision: None,
+            flags: CConversionFlags::empty(),
+        });
+        assert_eq!("%(amount)d".parse::<CFormatSpec>(), expected);
+
+        let expected = Ok(CFormatSpec {
+            mapping_key: Some("m((u(((l((((ti))))p)))l))e".to_owned()),
+            format_type: CFormatType::Number(CNumberType::Decimal),
+            format_char: 'd',
+            min_field_width: None,
+            precision: None,
+            flags: CConversionFlags::empty(),
+        });
+        assert_eq!(
+            "%(m((u(((l((((ti))))p)))l))e)d".parse::<CFormatSpec>(),
+            expected
+        );
+    }
+
+    #[test]
+    fn test_format_parse_key_fail() {
+        assert_eq!(
+            "%(aged".parse::<CFormatString>(),
+            Err(CFormatError {
+                typ: CFormatErrorType::UnmatchedKeyParentheses,
+                index: 1
+            })
+        );
+    }
+
+    #[test]
+    fn test_format_parse_type_fail() {
+        assert_eq!(
+            "Hello %n".parse::<CFormatString>(),
+            Err(CFormatError {
+                typ: CFormatErrorType::UnsupportedFormatChar('n'),
+                index: 7
+            })
+        );
+    }
+
+    #[test]
+    fn test_incomplete_format_fail() {
+        assert_eq!(
+            "Hello %".parse::<CFormatString>(),
+            Err(CFormatError {
+                typ: CFormatErrorType::IncompleteFormat,
+                index: 7
+            })
+        );
+    }
+
+    #[test]
+    fn test_parse_flags() {
+        let expected = Ok(CFormatSpec {
+            format_type: CFormatType::Number(CNumberType::Decimal),
+            format_char: 'd',
+            min_field_width: Some(CFormatQuantity::Amount(10)),
+            precision: None,
+            mapping_key: None,
+            flags: CConversionFlags::all(),
+        });
+        let parsed = "%  0   -+++###10d".parse::<CFormatSpec>();
+        assert_eq!(parsed, expected);
+        assert_eq!(
+            parsed.unwrap().format_number(&BigInt::from(12)),
+            "+12       ".to_owned()
+        );
+    }
+
+    #[test]
+    fn test_parse_and_format_string() {
+        assert_eq!(
+            "%5.4s"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_string("Hello, World!".to_owned()),
+            " Hell".to_owned()
+        );
+        assert_eq!(
+            "%-5.4s"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_string("Hello, World!".to_owned()),
+            "Hell ".to_owned()
+        );
+        assert_eq!(
+            "%.s"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_string("Hello, World!".to_owned()),
+            "".to_owned()
+        );
+        assert_eq!(
+            "%5.s"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_string("Hello, World!".to_owned()),
+            "     ".to_owned()
+        );
+    }
+
+    #[test]
+    fn test_parse_and_format_unicode_string() {
+        assert_eq!(
+            "%.2s"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_string("❤❤❤❤❤❤❤❤".to_owned()),
+            "❤❤".to_owned()
+        );
+    }
+
+    #[test]
+    fn test_parse_and_format_number() {
+        assert_eq!(
+            "%5d"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(27)),
+            "   27".to_owned()
+        );
+        assert_eq!(
+            "%05d"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(27)),
+            "00027".to_owned()
+        );
+        assert_eq!(
+            "%.5d"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(27)),
+            "00027".to_owned()
+        );
+        assert_eq!(
+            "%+05d"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(27)),
+            "+0027".to_owned()
+        );
+        assert_eq!(
+            "%-d"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(-27)),
+            "-27".to_owned()
+        );
+        assert_eq!(
+            "% d"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(27)),
+            " 27".to_owned()
+        );
+        assert_eq!(
+            "% d"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(-27)),
+            "-27".to_owned()
+        );
+        assert_eq!(
+            "%08x"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(0x1337)),
+            "00001337".to_owned()
+        );
+        assert_eq!(
+            "%#010x"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(0x1337)),
+            "0x00001337".to_owned()
+        );
+        assert_eq!(
+            "%-#010x"
+                .parse::<CFormatSpec>()
+                .unwrap()
+                .format_number(&BigInt::from(0x1337)),
+            "0x1337    ".to_owned()
+        );
+    }
+
+    #[test]
+    fn test_parse_and_format_float() {
+        assert_eq!(
+            "%f".parse::<CFormatSpec>().unwrap().format_float(1.2345),
+            "1.234500"
+        );
+        assert_eq!(
+            "%.2f".parse::<CFormatSpec>().unwrap().format_float(1.2345),
+            "1.23"
+        );
+        assert_eq!(
+            "%.f".parse::<CFormatSpec>().unwrap().format_float(1.2345),
+            "1"
+        );
+        assert_eq!(
+            "%+.f".parse::<CFormatSpec>().unwrap().format_float(1.2345),
+            "+1"
+        );
+        assert_eq!(
+            "%+f".parse::<CFormatSpec>().unwrap().format_float(1.2345),
+            "+1.234500"
+        );
+        assert_eq!(
+            "% f".parse::<CFormatSpec>().unwrap().format_float(1.2345),
+            " 1.234500"
+        );
+        assert_eq!(
+            "%f".parse::<CFormatSpec>().unwrap().format_float(-1.2345),
+            "-1.234500"
+        );
+        assert_eq!(
+            "%f".parse::<CFormatSpec>()
+                .unwrap()
+                .format_float(1.2345678901),
+            "1.234568"
+        );
+    }
+
+    #[test]
+    fn test_format_parse() {
+        let fmt = "Hello, my name is %s and I'm %d years old";
+        let expected = Ok(CFormatString {
+            parts: vec![
+                (0, CFormatPart::Literal("Hello, my name is ".to_owned())),
+                (
+                    18,
+                    CFormatPart::Spec(CFormatSpec {
+                        format_type: CFormatType::String(CFormatConversion::Str),
+                        format_char: 's',
+                        mapping_key: None,
+                        min_field_width: None,
+                        precision: None,
+                        flags: CConversionFlags::empty(),
+                    }),
+                ),
+                (20, CFormatPart::Literal(" and I'm ".to_owned())),
+                (
+                    29,
+                    CFormatPart::Spec(CFormatSpec {
+                        format_type: CFormatType::Number(CNumberType::Decimal),
+                        format_char: 'd',
+                        mapping_key: None,
+                        min_field_width: None,
+                        precision: None,
+                        flags: CConversionFlags::empty(),
+                    }),
+                ),
+                (31, CFormatPart::Literal(" years old".to_owned())),
+            ],
+        });
+        let result = fmt.parse::<CFormatString>();
+        assert_eq!(
+            result, expected,
+            "left = {result:#?} \n\n\n right = {expected:#?}"
+        );
+    }
+}
diff --git a/literal/src/format.rs b/literal/src/format.rs
index 3d5d9d7..8764c35 100644
--- a/literal/src/format.rs
+++ b/literal/src/format.rs
@@ -1,5 +1,1229 @@
+use crate::float;
+use itertools::{Itertools, PeekingNext};
+use num_bigint::{BigInt, Sign};
+use num_traits::{cast::ToPrimitive, Signed};
+use std::ops::Deref;
+use std::{cmp, str::FromStr};
+
 #[derive(Debug, PartialEq, Clone, Copy)]
 pub enum Case {
     Lower,
     Upper,
 }
+
+trait FormatParse {
+    fn parse(text: &str) -> (Option<Self>, &str)
+    where
+        Self: Sized;
+}
+
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum FormatConversion {
+    Str,
+    Repr,
+    Ascii,
+    Bytes,
+}
+
+impl FormatParse for FormatConversion {
+    fn parse(text: &str) -> (Option<Self>, &str) {
+        let Some(conversion) = Self::from_string(text) else {
+            return (None, text);
+        };
+        let mut chars = text.chars();
+        chars.next(); // Consume the bang
+        chars.next(); // Consume one r,s,a char
+        (Some(conversion), chars.as_str())
+    }
+}
+
+impl FormatConversion {
+    pub fn from_char(c: char) -> Option<FormatConversion> {
+        match c {
+            's' => Some(FormatConversion::Str),
+            'r' => Some(FormatConversion::Repr),
+            'a' => Some(FormatConversion::Ascii),
+            'b' => Some(FormatConversion::Bytes),
+            _ => None,
+        }
+    }
+
+    fn from_string(text: &str) -> Option<FormatConversion> {
+        let mut chars = text.chars();
+        if chars.next() != Some('!') {
+            return None;
+        }
+
+        FormatConversion::from_char(chars.next()?)
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum FormatAlign {
+    Left,
+    Right,
+    AfterSign,
+    Center,
+}
+
+impl FormatAlign {
+    fn from_char(c: char) -> Option<FormatAlign> {
+        match c {
+            '<' => Some(FormatAlign::Left),
+            '>' => Some(FormatAlign::Right),
+            '=' => Some(FormatAlign::AfterSign),
+            '^' => Some(FormatAlign::Center),
+            _ => None,
+        }
+    }
+}
+
+impl FormatParse for FormatAlign {
+    fn parse(text: &str) -> (Option<Self>, &str) {
+        let mut chars = text.chars();
+        if let Some(maybe_align) = chars.next().and_then(Self::from_char) {
+            (Some(maybe_align), chars.as_str())
+        } else {
+            (None, text)
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum FormatSign {
+    Plus,
+    Minus,
+    MinusOrSpace,
+}
+
+impl FormatParse for FormatSign {
+    fn parse(text: &str) -> (Option<Self>, &str) {
+        let mut chars = text.chars();
+        match chars.next() {
+            Some('-') => (Some(Self::Minus), chars.as_str()),
+            Some('+') => (Some(Self::Plus), chars.as_str()),
+            Some(' ') => (Some(Self::MinusOrSpace), chars.as_str()),
+            _ => (None, text),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum FormatGrouping {
+    Comma,
+    Underscore,
+}
+
+impl FormatParse for FormatGrouping {
+    fn parse(text: &str) -> (Option<Self>, &str) {
+        let mut chars = text.chars();
+        match chars.next() {
+            Some('_') => (Some(Self::Underscore), chars.as_str()),
+            Some(',') => (Some(Self::Comma), chars.as_str()),
+            _ => (None, text),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum FormatType {
+    String,
+    Binary,
+    Character,
+    Decimal,
+    Octal,
+    Number(Case),
+    Hex(Case),
+    Exponent(Case),
+    GeneralFormat(Case),
+    FixedPoint(Case),
+    Percentage,
+}
+
+impl From<&FormatType> for char {
+    fn from(from: &FormatType) -> char {
+        match from {
+            FormatType::String => 's',
+            FormatType::Binary => 'b',
+            FormatType::Character => 'c',
+            FormatType::Decimal => 'd',
+            FormatType::Octal => 'o',
+            FormatType::Number(Case::Lower) => 'n',
+            FormatType::Number(Case::Upper) => 'N',
+            FormatType::Hex(Case::Lower) => 'x',
+            FormatType::Hex(Case::Upper) => 'X',
+            FormatType::Exponent(Case::Lower) => 'e',
+            FormatType::Exponent(Case::Upper) => 'E',
+            FormatType::GeneralFormat(Case::Lower) => 'g',
+            FormatType::GeneralFormat(Case::Upper) => 'G',
+            FormatType::FixedPoint(Case::Lower) => 'f',
+            FormatType::FixedPoint(Case::Upper) => 'F',
+            FormatType::Percentage => '%',
+        }
+    }
+}
+
+impl FormatParse for FormatType {
+    fn parse(text: &str) -> (Option<Self>, &str) {
+        let mut chars = text.chars();
+        match chars.next() {
+            Some('s') => (Some(Self::String), chars.as_str()),
+            Some('b') => (Some(Self::Binary), chars.as_str()),
+            Some('c') => (Some(Self::Character), chars.as_str()),
+            Some('d') => (Some(Self::Decimal), chars.as_str()),
+            Some('o') => (Some(Self::Octal), chars.as_str()),
+            Some('n') => (Some(Self::Number(Case::Lower)), chars.as_str()),
+            Some('N') => (Some(Self::Number(Case::Upper)), chars.as_str()),
+            Some('x') => (Some(Self::Hex(Case::Lower)), chars.as_str()),
+            Some('X') => (Some(Self::Hex(Case::Upper)), chars.as_str()),
+            Some('e') => (Some(Self::Exponent(Case::Lower)), chars.as_str()),
+            Some('E') => (Some(Self::Exponent(Case::Upper)), chars.as_str()),
+            Some('f') => (Some(Self::FixedPoint(Case::Lower)), chars.as_str()),
+            Some('F') => (Some(Self::FixedPoint(Case::Upper)), chars.as_str()),
+            Some('g') => (Some(Self::GeneralFormat(Case::Lower)), chars.as_str()),
+            Some('G') => (Some(Self::GeneralFormat(Case::Upper)), chars.as_str()),
+            Some('%') => (Some(Self::Percentage), chars.as_str()),
+            _ => (None, text),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct FormatSpec {
+    conversion: Option<FormatConversion>,
+    fill: Option<char>,
+    align: Option<FormatAlign>,
+    sign: Option<FormatSign>,
+    alternate_form: bool,
+    width: Option<usize>,
+    grouping_option: Option<FormatGrouping>,
+    precision: Option<usize>,
+    format_type: Option<FormatType>,
+}
+
+fn get_num_digits(text: &str) -> usize {
+    for (index, character) in text.char_indices() {
+        if !character.is_ascii_digit() {
+            return index;
+        }
+    }
+    text.len()
+}
+
+fn parse_fill_and_align(text: &str) -> (Option<char>, Option<FormatAlign>, &str) {
+    let char_indices: Vec<(usize, char)> = text.char_indices().take(3).collect();
+    if char_indices.is_empty() {
+        (None, None, text)
+    } else if char_indices.len() == 1 {
+        let (maybe_align, remaining) = FormatAlign::parse(text);
+        (None, maybe_align, remaining)
+    } else {
+        let (maybe_align, remaining) = FormatAlign::parse(&text[char_indices[1].0..]);
+        if maybe_align.is_some() {
+            (Some(char_indices[0].1), maybe_align, remaining)
+        } else {
+            let (only_align, only_align_remaining) = FormatAlign::parse(text);
+            (None, only_align, only_align_remaining)
+        }
+    }
+}
+
+fn parse_number(text: &str) -> Result<(Option<usize>, &str), FormatSpecError> {
+    let num_digits: usize = get_num_digits(text);
+    if num_digits == 0 {
+        return Ok((None, text));
+    }
+    if let Ok(num) = text[..num_digits].parse::<usize>() {
+        Ok((Some(num), &text[num_digits..]))
+    } else {
+        // NOTE: this condition is different from CPython
+        Err(FormatSpecError::DecimalDigitsTooMany)
+    }
+}
+
+fn parse_alternate_form(text: &str) -> (bool, &str) {
+    let mut chars = text.chars();
+    match chars.next() {
+        Some('#') => (true, chars.as_str()),
+        _ => (false, text),
+    }
+}
+
+fn parse_zero(text: &str) -> (bool, &str) {
+    let mut chars = text.chars();
+    match chars.next() {
+        Some('0') => (true, chars.as_str()),
+        _ => (false, text),
+    }
+}
+
+fn parse_precision(text: &str) -> Result<(Option<usize>, &str), FormatSpecError> {
+    let mut chars = text.chars();
+    Ok(match chars.next() {
+        Some('.') => {
+            let (size, remaining) = parse_number(chars.as_str())?;
+            if let Some(size) = size {
+                if size > i32::MAX as usize {
+                    return Err(FormatSpecError::PrecisionTooBig);
+                }
+                (Some(size), remaining)
+            } else {
+                (None, text)
+            }
+        }
+        _ => (None, text),
+    })
+}
+
+impl FormatSpec {
+    pub fn parse(text: &str) -> Result<Self, FormatSpecError> {
+        // get_integer in CPython
+        let (conversion, text) = FormatConversion::parse(text);
+        let (mut fill, mut align, text) = parse_fill_and_align(text);
+        let (sign, text) = FormatSign::parse(text);
+        let (alternate_form, text) = parse_alternate_form(text);
+        let (zero, text) = parse_zero(text);
+        let (width, text) = parse_number(text)?;
+        let (grouping_option, text) = FormatGrouping::parse(text);
+        let (precision, text) = parse_precision(text)?;
+        let (format_type, text) = FormatType::parse(text);
+        if !text.is_empty() {
+            return Err(FormatSpecError::InvalidFormatSpecifier);
+        }
+
+        if zero && fill.is_none() {
+            fill.replace('0');
+            align = align.or(Some(FormatAlign::AfterSign));
+        }
+
+        Ok(FormatSpec {
+            conversion,
+            fill,
+            align,
+            sign,
+            alternate_form,
+            width,
+            grouping_option,
+            precision,
+            format_type,
+        })
+    }
+
+    fn compute_fill_string(fill_char: char, fill_chars_needed: i32) -> String {
+        (0..fill_chars_needed)
+            .map(|_| fill_char)
+            .collect::<String>()
+    }
+
+    fn add_magnitude_separators_for_char(
+        magnitude_str: String,
+        inter: i32,
+        sep: char,
+        disp_digit_cnt: i32,
+    ) -> String {
+        // Don't add separators to the floating decimal point of numbers
+        let mut parts = magnitude_str.splitn(2, '.');
+        let magnitude_int_str = parts.next().unwrap().to_string();
+        let dec_digit_cnt = magnitude_str.len() as i32 - magnitude_int_str.len() as i32;
+        let int_digit_cnt = disp_digit_cnt - dec_digit_cnt;
+        let mut result = FormatSpec::separate_integer(magnitude_int_str, inter, sep, int_digit_cnt);
+        if let Some(part) = parts.next() {
+            result.push_str(&format!(".{part}"))
+        }
+        result
+    }
+
+    fn separate_integer(
+        magnitude_str: String,
+        inter: i32,
+        sep: char,
+        disp_digit_cnt: i32,
+    ) -> String {
+        let magnitude_len = magnitude_str.len() as i32;
+        let offset = (disp_digit_cnt % (inter + 1) == 0) as i32;
+        let disp_digit_cnt = disp_digit_cnt + offset;
+        let pad_cnt = disp_digit_cnt - magnitude_len;
+        let sep_cnt = disp_digit_cnt / (inter + 1);
+        let diff = pad_cnt - sep_cnt;
+        if pad_cnt > 0 && diff > 0 {
+            // separate with 0 padding
+            let padding = "0".repeat(diff as usize);
+            let padded_num = format!("{padding}{magnitude_str}");
+            FormatSpec::insert_separator(padded_num, inter, sep, sep_cnt)
+        } else {
+            // separate without padding
+            let sep_cnt = (magnitude_len - 1) / inter;
+            FormatSpec::insert_separator(magnitude_str, inter, sep, sep_cnt)
+        }
+    }
+
+    fn insert_separator(mut magnitude_str: String, inter: i32, sep: char, sep_cnt: i32) -> String {
+        let magnitude_len = magnitude_str.len() as i32;
+        for i in 1..sep_cnt + 1 {
+            magnitude_str.insert((magnitude_len - inter * i) as usize, sep);
+        }
+        magnitude_str
+    }
+
+    fn validate_format(&self, default_format_type: FormatType) -> Result<(), FormatSpecError> {
+        let format_type = self.format_type.as_ref().unwrap_or(&default_format_type);
+        match (&self.grouping_option, format_type) {
+            (
+                Some(FormatGrouping::Comma),
+                FormatType::String
+                | FormatType::Character
+                | FormatType::Binary
+                | FormatType::Octal
+                | FormatType::Hex(_)
+                | FormatType::Number(_),
+            ) => {
+                let ch = char::from(format_type);
+                Err(FormatSpecError::UnspecifiedFormat(',', ch))
+            }
+            (
+                Some(FormatGrouping::Underscore),
+                FormatType::String | FormatType::Character | FormatType::Number(_),
+            ) => {
+                let ch = char::from(format_type);
+                Err(FormatSpecError::UnspecifiedFormat('_', ch))
+            }
+            _ => Ok(()),
+        }
+    }
+
+    fn get_separator_interval(&self) -> usize {
+        match self.format_type {
+            Some(FormatType::Binary | FormatType::Octal | FormatType::Hex(_)) => 4,
+            Some(FormatType::Decimal | FormatType::Number(_) | FormatType::FixedPoint(_)) => 3,
+            None => 3,
+            _ => panic!("Separators only valid for numbers!"),
+        }
+    }
+
+    fn add_magnitude_separators(&self, magnitude_str: String, prefix: &str) -> String {
+        match &self.grouping_option {
+            Some(fg) => {
+                let sep = match fg {
+                    FormatGrouping::Comma => ',',
+                    FormatGrouping::Underscore => '_',
+                };
+                let inter = self.get_separator_interval().try_into().unwrap();
+                let magnitude_len = magnitude_str.len();
+                let width = self.width.unwrap_or(magnitude_len) as i32 - prefix.len() as i32;
+                let disp_digit_cnt = cmp::max(width, magnitude_len as i32);
+                FormatSpec::add_magnitude_separators_for_char(
+                    magnitude_str,
+                    inter,
+                    sep,
+                    disp_digit_cnt,
+                )
+            }
+            None => magnitude_str,
+        }
+    }
+
+    pub fn format_bool(&self, input: bool) -> Result<String, FormatSpecError> {
+        let x = u8::from(input);
+        let result: Result<String, FormatSpecError> = match &self.format_type {
+            Some(FormatType::Decimal) => Ok(x.to_string()),
+            None => {
+                let first_letter = (input.to_string().as_bytes()[0] as char).to_uppercase();
+                Ok(first_letter.collect::<String>() + &input.to_string()[1..])
+            }
+            _ => Err(FormatSpecError::InvalidFormatSpecifier),
+        };
+        result
+    }
+
+    pub fn format_float(&self, num: f64) -> Result<String, FormatSpecError> {
+        self.validate_format(FormatType::FixedPoint(Case::Lower))?;
+        let precision = self.precision.unwrap_or(6);
+        let magnitude = num.abs();
+        let raw_magnitude_str: Result<String, FormatSpecError> = match &self.format_type {
+            Some(FormatType::FixedPoint(case)) => Ok(float::format_fixed(
+                precision,
+                magnitude,
+                *case,
+                self.alternate_form,
+            )),
+            Some(FormatType::Decimal)
+            | Some(FormatType::Binary)
+            | Some(FormatType::Octal)
+            | Some(FormatType::Hex(_))
+            | Some(FormatType::String)
+            | Some(FormatType::Character)
+            | Some(FormatType::Number(Case::Upper)) => {
+                let ch = char::from(self.format_type.as_ref().unwrap());
+                Err(FormatSpecError::UnknownFormatCode(ch, "float"))
+            }
+            Some(FormatType::GeneralFormat(case)) | Some(FormatType::Number(case)) => {
+                let precision = if precision == 0 { 1 } else { precision };
+                Ok(float::format_general(
+                    precision,
+                    magnitude,
+                    *case,
+                    self.alternate_form,
+                    false,
+                ))
+            }
+            Some(FormatType::Exponent(case)) => Ok(float::format_exponent(
+                precision,
+                magnitude,
+                *case,
+                self.alternate_form,
+            )),
+            Some(FormatType::Percentage) => match magnitude {
+                magnitude if magnitude.is_nan() => Ok("nan%".to_owned()),
+                magnitude if magnitude.is_infinite() => Ok("inf%".to_owned()),
+                _ => {
+                    let result = format!("{:.*}", precision, magnitude * 100.0);
+                    let point = float::decimal_point_or_empty(precision, self.alternate_form);
+                    Ok(format!("{result}{point}%"))
+                }
+            },
+            None => match magnitude {
+                magnitude if magnitude.is_nan() => Ok("nan".to_owned()),
+                magnitude if magnitude.is_infinite() => Ok("inf".to_owned()),
+                _ => match self.precision {
+                    Some(precision) => Ok(float::format_general(
+                        precision,
+                        magnitude,
+                        Case::Lower,
+                        self.alternate_form,
+                        true,
+                    )),
+                    None => Ok(float::to_string(magnitude)),
+                },
+            },
+        };
+        let format_sign = self.sign.unwrap_or(FormatSign::Minus);
+        let sign_str = if num.is_sign_negative() && !num.is_nan() {
+            "-"
+        } else {
+            match format_sign {
+                FormatSign::Plus => "+",
+                FormatSign::Minus => "",
+                FormatSign::MinusOrSpace => " ",
+            }
+        };
+        let magnitude_str = self.add_magnitude_separators(raw_magnitude_str?, sign_str);
+        self.format_sign_and_align(&AsciiStr::new(&magnitude_str), sign_str, FormatAlign::Right)
+    }
+
+    #[inline]
+    fn format_int_radix(&self, magnitude: BigInt, radix: u32) -> Result<String, FormatSpecError> {
+        match self.precision {
+            Some(_) => Err(FormatSpecError::PrecisionNotAllowed),
+            None => Ok(magnitude.to_str_radix(radix)),
+        }
+    }
+
+    pub fn format_int(&self, num: &BigInt) -> Result<String, FormatSpecError> {
+        self.validate_format(FormatType::Decimal)?;
+        let magnitude = num.abs();
+        let prefix = if self.alternate_form {
+            match self.format_type {
+                Some(FormatType::Binary) => "0b",
+                Some(FormatType::Octal) => "0o",
+                Some(FormatType::Hex(Case::Lower)) => "0x",
+                Some(FormatType::Hex(Case::Upper)) => "0X",
+                _ => "",
+            }
+        } else {
+            ""
+        };
+        let raw_magnitude_str = match self.format_type {
+            Some(FormatType::Binary) => self.format_int_radix(magnitude, 2),
+            Some(FormatType::Decimal) => self.format_int_radix(magnitude, 10),
+            Some(FormatType::Octal) => self.format_int_radix(magnitude, 8),
+            Some(FormatType::Hex(Case::Lower)) => self.format_int_radix(magnitude, 16),
+            Some(FormatType::Hex(Case::Upper)) => match self.precision {
+                Some(_) => Err(FormatSpecError::PrecisionNotAllowed),
+                None => {
+                    let mut result = magnitude.to_str_radix(16);
+                    result.make_ascii_uppercase();
+                    Ok(result)
+                }
+            },
+            Some(FormatType::Number(Case::Lower)) => self.format_int_radix(magnitude, 10),
+            Some(FormatType::Number(Case::Upper)) => {
+                Err(FormatSpecError::UnknownFormatCode('N', "int"))
+            }
+            Some(FormatType::String) => Err(FormatSpecError::UnknownFormatCode('s', "int")),
+            Some(FormatType::Character) => match (self.sign, self.alternate_form) {
+                (Some(_), _) => Err(FormatSpecError::NotAllowed("Sign")),
+                (_, true) => Err(FormatSpecError::NotAllowed("Alternate form (#)")),
+                (_, _) => match num.to_u32() {
+                    Some(n) if n <= 0x10ffff => Ok(std::char::from_u32(n).unwrap().to_string()),
+                    Some(_) | None => Err(FormatSpecError::CodeNotInRange),
+                },
+            },
+            Some(FormatType::GeneralFormat(_))
+            | Some(FormatType::FixedPoint(_))
+            | Some(FormatType::Exponent(_))
+            | Some(FormatType::Percentage) => match num.to_f64() {
+                Some(float) => return self.format_float(float),
+                _ => Err(FormatSpecError::UnableToConvert),
+            },
+            None => self.format_int_radix(magnitude, 10),
+        }?;
+        let format_sign = self.sign.unwrap_or(FormatSign::Minus);
+        let sign_str = match num.sign() {
+            Sign::Minus => "-",
+            _ => match format_sign {
+                FormatSign::Plus => "+",
+                FormatSign::Minus => "",
+                FormatSign::MinusOrSpace => " ",
+            },
+        };
+        let sign_prefix = format!("{sign_str}{prefix}");
+        let magnitude_str = self.add_magnitude_separators(raw_magnitude_str, &sign_prefix);
+        self.format_sign_and_align(
+            &AsciiStr::new(&magnitude_str),
+            &sign_prefix,
+            FormatAlign::Right,
+        )
+    }
+
+    pub fn format_string<T>(&self, s: &T) -> Result<String, FormatSpecError>
+    where
+        T: CharLen + Deref<Target = str>,
+    {
+        self.validate_format(FormatType::String)?;
+        match self.format_type {
+            Some(FormatType::String) | None => self
+                .format_sign_and_align(s, "", FormatAlign::Left)
+                .map(|mut value| {
+                    if let Some(precision) = self.precision {
+                        value.truncate(precision);
+                    }
+                    value
+                }),
+            _ => {
+                let ch = char::from(self.format_type.as_ref().unwrap());
+                Err(FormatSpecError::UnknownFormatCode(ch, "str"))
+            }
+        }
+    }
+
+    fn format_sign_and_align<T>(
+        &self,
+        magnitude_str: &T,
+        sign_str: &str,
+        default_align: FormatAlign,
+    ) -> Result<String, FormatSpecError>
+    where
+        T: CharLen + Deref<Target = str>,
+    {
+        let align = self.align.unwrap_or(default_align);
+
+        let num_chars = magnitude_str.char_len();
+        let fill_char = self.fill.unwrap_or(' ');
+        let fill_chars_needed: i32 = self.width.map_or(0, |w| {
+            cmp::max(0, (w as i32) - (num_chars as i32) - (sign_str.len() as i32))
+        });
+
+        let magnitude_str = magnitude_str.deref();
+        Ok(match align {
+            FormatAlign::Left => format!(
+                "{}{}{}",
+                sign_str,
+                magnitude_str,
+                FormatSpec::compute_fill_string(fill_char, fill_chars_needed)
+            ),
+            FormatAlign::Right => format!(
+                "{}{}{}",
+                FormatSpec::compute_fill_string(fill_char, fill_chars_needed),
+                sign_str,
+                magnitude_str
+            ),
+            FormatAlign::AfterSign => format!(
+                "{}{}{}",
+                sign_str,
+                FormatSpec::compute_fill_string(fill_char, fill_chars_needed),
+                magnitude_str
+            ),
+            FormatAlign::Center => {
+                let left_fill_chars_needed = fill_chars_needed / 2;
+                let right_fill_chars_needed = fill_chars_needed - left_fill_chars_needed;
+                let left_fill_string =
+                    FormatSpec::compute_fill_string(fill_char, left_fill_chars_needed);
+                let right_fill_string =
+                    FormatSpec::compute_fill_string(fill_char, right_fill_chars_needed);
+                format!("{left_fill_string}{sign_str}{magnitude_str}{right_fill_string}")
+            }
+        })
+    }
+}
+
+pub trait CharLen {
+    /// Returns the number of characters in the text
+    fn char_len(&self) -> usize;
+}
+
+struct AsciiStr<'a> {
+    inner: &'a str,
+}
+
+impl<'a> AsciiStr<'a> {
+    fn new(inner: &'a str) -> Self {
+        Self { inner }
+    }
+}
+
+impl CharLen for AsciiStr<'_> {
+    fn char_len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl Deref for AsciiStr<'_> {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.inner
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum FormatSpecError {
+    DecimalDigitsTooMany,
+    PrecisionTooBig,
+    InvalidFormatSpecifier,
+    UnspecifiedFormat(char, char),
+    UnknownFormatCode(char, &'static str),
+    PrecisionNotAllowed,
+    NotAllowed(&'static str),
+    UnableToConvert,
+    CodeNotInRange,
+    NotImplemented(char, &'static str),
+}
+
+#[derive(Debug, PartialEq)]
+pub enum FormatParseError {
+    UnmatchedBracket,
+    MissingStartBracket,
+    UnescapedStartBracketInLiteral,
+    InvalidFormatSpecifier,
+    UnknownConversion,
+    EmptyAttribute,
+    MissingRightBracket,
+    InvalidCharacterAfterRightBracket,
+}
+
+impl FromStr for FormatSpec {
+    type Err = FormatSpecError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        FormatSpec::parse(s)
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum FieldNamePart {
+    Attribute(String),
+    Index(usize),
+    StringIndex(String),
+}
+
+impl FieldNamePart {
+    fn parse_part(
+        chars: &mut impl PeekingNext<Item = char>,
+    ) -> Result<Option<FieldNamePart>, FormatParseError> {
+        chars
+            .next()
+            .map(|ch| match ch {
+                '.' => {
+                    let mut attribute = String::new();
+                    for ch in chars.peeking_take_while(|ch| *ch != '.' && *ch != '[') {
+                        attribute.push(ch);
+                    }
+                    if attribute.is_empty() {
+                        Err(FormatParseError::EmptyAttribute)
+                    } else {
+                        Ok(FieldNamePart::Attribute(attribute))
+                    }
+                }
+                '[' => {
+                    let mut index = String::new();
+                    for ch in chars {
+                        if ch == ']' {
+                            return if index.is_empty() {
+                                Err(FormatParseError::EmptyAttribute)
+                            } else if let Ok(index) = index.parse::<usize>() {
+                                Ok(FieldNamePart::Index(index))
+                            } else {
+                                Ok(FieldNamePart::StringIndex(index))
+                            };
+                        }
+                        index.push(ch);
+                    }
+                    Err(FormatParseError::MissingRightBracket)
+                }
+                _ => Err(FormatParseError::InvalidCharacterAfterRightBracket),
+            })
+            .transpose()
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum FieldType {
+    Auto,
+    Index(usize),
+    Keyword(String),
+}
+
+#[derive(Debug, PartialEq)]
+pub struct FieldName {
+    pub field_type: FieldType,
+    pub parts: Vec<FieldNamePart>,
+}
+
+impl FieldName {
+    pub fn parse(text: &str) -> Result<FieldName, FormatParseError> {
+        let mut chars = text.chars().peekable();
+        let mut first = String::new();
+        for ch in chars.peeking_take_while(|ch| *ch != '.' && *ch != '[') {
+            first.push(ch);
+        }
+
+        let field_type = if first.is_empty() {
+            FieldType::Auto
+        } else if let Ok(index) = first.parse::<usize>() {
+            FieldType::Index(index)
+        } else {
+            FieldType::Keyword(first)
+        };
+
+        let mut parts = Vec::new();
+        while let Some(part) = FieldNamePart::parse_part(&mut chars)? {
+            parts.push(part)
+        }
+
+        Ok(FieldName { field_type, parts })
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum FormatPart {
+    Field {
+        field_name: String,
+        conversion_spec: Option<char>,
+        format_spec: String,
+    },
+    Literal(String),
+}
+
+#[derive(Debug, PartialEq)]
+pub struct FormatString {
+    pub format_parts: Vec<FormatPart>,
+}
+
+impl FormatString {
+    fn parse_literal_single(text: &str) -> Result<(char, &str), FormatParseError> {
+        let mut chars = text.chars();
+        // This should never be called with an empty str
+        let first_char = chars.next().unwrap();
+        // isn't this detectable only with bytes operation?
+        if first_char == '{' || first_char == '}' {
+            let maybe_next_char = chars.next();
+            // if we see a bracket, it has to be escaped by doubling up to be in a literal
+            return if maybe_next_char.is_none() || maybe_next_char.unwrap() != first_char {
+                Err(FormatParseError::UnescapedStartBracketInLiteral)
+            } else {
+                Ok((first_char, chars.as_str()))
+            };
+        }
+        Ok((first_char, chars.as_str()))
+    }
+
+    fn parse_literal(text: &str) -> Result<(FormatPart, &str), FormatParseError> {
+        let mut cur_text = text;
+        let mut result_string = String::new();
+        while !cur_text.is_empty() {
+            match FormatString::parse_literal_single(cur_text) {
+                Ok((next_char, remaining)) => {
+                    result_string.push(next_char);
+                    cur_text = remaining;
+                }
+                Err(err) => {
+                    return if !result_string.is_empty() {
+                        Ok((FormatPart::Literal(result_string), cur_text))
+                    } else {
+                        Err(err)
+                    };
+                }
+            }
+        }
+        Ok((FormatPart::Literal(result_string), ""))
+    }
+
+    fn parse_part_in_brackets(text: &str) -> Result<FormatPart, FormatParseError> {
+        let parts: Vec<&str> = text.splitn(2, ':').collect();
+        // before the comma is a keyword or arg index, after the comma is maybe a spec.
+        let arg_part = parts[0];
+
+        let format_spec = if parts.len() > 1 {
+            parts[1].to_owned()
+        } else {
+            String::new()
+        };
+
+        // On parts[0] can still be the conversion (!r, !s, !a)
+        let parts: Vec<&str> = arg_part.splitn(2, '!').collect();
+        // before the bang is a keyword or arg index, after the comma is maybe a conversion spec.
+        let arg_part = parts[0];
+
+        let conversion_spec = parts
+            .get(1)
+            .map(|conversion| {
+                // conversions are only every one character
+                conversion
+                    .chars()
+                    .exactly_one()
+                    .map_err(|_| FormatParseError::UnknownConversion)
+            })
+            .transpose()?;
+
+        Ok(FormatPart::Field {
+            field_name: arg_part.to_owned(),
+            conversion_spec,
+            format_spec,
+        })
+    }
+
+    fn parse_spec(text: &str) -> Result<(FormatPart, &str), FormatParseError> {
+        let mut nested = false;
+        let mut end_bracket_pos = None;
+        let mut left = String::new();
+
+        // There may be one layer nesting brackets in spec
+        for (idx, c) in text.char_indices() {
+            if idx == 0 {
+                if c != '{' {
+                    return Err(FormatParseError::MissingStartBracket);
+                }
+            } else if c == '{' {
+                if nested {
+                    return Err(FormatParseError::InvalidFormatSpecifier);
+                } else {
+                    nested = true;
+                    left.push(c);
+                    continue;
+                }
+            } else if c == '}' {
+                if nested {
+                    nested = false;
+                    left.push(c);
+                    continue;
+                } else {
+                    end_bracket_pos = Some(idx);
+                    break;
+                }
+            } else {
+                left.push(c);
+            }
+        }
+        if let Some(pos) = end_bracket_pos {
+            let (_, right) = text.split_at(pos);
+            let format_part = FormatString::parse_part_in_brackets(&left)?;
+            Ok((format_part, &right[1..]))
+        } else {
+            Err(FormatParseError::UnmatchedBracket)
+        }
+    }
+}
+
+pub trait FromTemplate<'a>: Sized {
+    type Err;
+    fn from_str(s: &'a str) -> Result<Self, Self::Err>;
+}
+
+impl<'a> FromTemplate<'a> for FormatString {
+    type Err = FormatParseError;
+
+    fn from_str(text: &'a str) -> Result<Self, Self::Err> {
+        let mut cur_text: &str = text;
+        let mut parts: Vec<FormatPart> = Vec::new();
+        while !cur_text.is_empty() {
+            // Try to parse both literals and bracketed format parts until we
+            // run out of text
+            cur_text = FormatString::parse_literal(cur_text)
+                .or_else(|_| FormatString::parse_spec(cur_text))
+                .map(|(part, new_text)| {
+                    parts.push(part);
+                    new_text
+                })?;
+        }
+        Ok(FormatString {
+            format_parts: parts,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_fill_and_align() {
+        assert_eq!(
+            parse_fill_and_align(" <"),
+            (Some(' '), Some(FormatAlign::Left), "")
+        );
+        assert_eq!(
+            parse_fill_and_align(" <22"),
+            (Some(' '), Some(FormatAlign::Left), "22")
+        );
+        assert_eq!(
+            parse_fill_and_align("<22"),
+            (None, Some(FormatAlign::Left), "22")
+        );
+        assert_eq!(
+            parse_fill_and_align(" ^^"),
+            (Some(' '), Some(FormatAlign::Center), "^")
+        );
+        assert_eq!(
+            parse_fill_and_align("==="),
+            (Some('='), Some(FormatAlign::AfterSign), "=")
+        );
+    }
+
+    #[test]
+    fn test_width_only() {
+        let expected = Ok(FormatSpec {
+            conversion: None,
+            fill: None,
+            align: None,
+            sign: None,
+            alternate_form: false,
+            width: Some(33),
+            grouping_option: None,
+            precision: None,
+            format_type: None,
+        });
+        assert_eq!(FormatSpec::parse("33"), expected);
+    }
+
+    #[test]
+    fn test_fill_and_width() {
+        let expected = Ok(FormatSpec {
+            conversion: None,
+            fill: Some('<'),
+            align: Some(FormatAlign::Right),
+            sign: None,
+            alternate_form: false,
+            width: Some(33),
+            grouping_option: None,
+            precision: None,
+            format_type: None,
+        });
+        assert_eq!(FormatSpec::parse("<>33"), expected);
+    }
+
+    #[test]
+    fn test_all() {
+        let expected = Ok(FormatSpec {
+            conversion: None,
+            fill: Some('<'),
+            align: Some(FormatAlign::Right),
+            sign: Some(FormatSign::Minus),
+            alternate_form: true,
+            width: Some(23),
+            grouping_option: Some(FormatGrouping::Comma),
+            precision: Some(11),
+            format_type: Some(FormatType::Binary),
+        });
+        assert_eq!(FormatSpec::parse("<>-#23,.11b"), expected);
+    }
+
+    #[test]
+    fn test_format_int() {
+        assert_eq!(
+            FormatSpec::parse("d")
+                .unwrap()
+                .format_int(&BigInt::from_bytes_be(Sign::Plus, b"\x10")),
+            Ok("16".to_owned())
+        );
+        assert_eq!(
+            FormatSpec::parse("x")
+                .unwrap()
+                .format_int(&BigInt::from_bytes_be(Sign::Plus, b"\x10")),
+            Ok("10".to_owned())
+        );
+        assert_eq!(
+            FormatSpec::parse("b")
+                .unwrap()
+                .format_int(&BigInt::from_bytes_be(Sign::Plus, b"\x10")),
+            Ok("10000".to_owned())
+        );
+        assert_eq!(
+            FormatSpec::parse("o")
+                .unwrap()
+                .format_int(&BigInt::from_bytes_be(Sign::Plus, b"\x10")),
+            Ok("20".to_owned())
+        );
+        assert_eq!(
+            FormatSpec::parse("+d")
+                .unwrap()
+                .format_int(&BigInt::from_bytes_be(Sign::Plus, b"\x10")),
+            Ok("+16".to_owned())
+        );
+        assert_eq!(
+            FormatSpec::parse("^ 5d")
+                .unwrap()
+                .format_int(&BigInt::from_bytes_be(Sign::Minus, b"\x10")),
+            Ok(" -16 ".to_owned())
+        );
+        assert_eq!(
+            FormatSpec::parse("0>+#10x")
+                .unwrap()
+                .format_int(&BigInt::from_bytes_be(Sign::Plus, b"\x10")),
+            Ok("00000+0x10".to_owned())
+        );
+    }
+
+    #[test]
+    fn test_format_int_sep() {
+        let spec = FormatSpec::parse(",").expect("");
+        assert_eq!(spec.grouping_option, Some(FormatGrouping::Comma));
+        assert_eq!(
+            spec.format_int(&BigInt::from_str("1234567890123456789012345678").unwrap()),
+            Ok("1,234,567,890,123,456,789,012,345,678".to_owned())
+        );
+    }
+
+    #[test]
+    fn test_format_parse() {
+        let expected = Ok(FormatString {
+            format_parts: vec![
+                FormatPart::Literal("abcd".to_owned()),
+                FormatPart::Field {
+                    field_name: "1".to_owned(),
+                    conversion_spec: None,
+                    format_spec: String::new(),
+                },
+                FormatPart::Literal(":".to_owned()),
+                FormatPart::Field {
+                    field_name: "key".to_owned(),
+                    conversion_spec: None,
+                    format_spec: String::new(),
+                },
+            ],
+        });
+
+        assert_eq!(FormatString::from_str("abcd{1}:{key}"), expected);
+    }
+
+    #[test]
+    fn test_format_parse_multi_byte_char() {
+        assert!(FormatString::from_str("{a:%ЫйЯЧ}").is_ok());
+    }
+
+    #[test]
+    fn test_format_parse_fail() {
+        assert_eq!(
+            FormatString::from_str("{s"),
+            Err(FormatParseError::UnmatchedBracket)
+        );
+    }
+
+    #[test]
+    fn test_format_parse_escape() {
+        let expected = Ok(FormatString {
+            format_parts: vec![
+                FormatPart::Literal("{".to_owned()),
+                FormatPart::Field {
+                    field_name: "key".to_owned(),
+                    conversion_spec: None,
+                    format_spec: String::new(),
+                },
+                FormatPart::Literal("}ddfe".to_owned()),
+            ],
+        });
+
+        assert_eq!(FormatString::from_str("{{{key}}}ddfe"), expected);
+    }
+
+    #[test]
+    fn test_format_invalid_specification() {
+        assert_eq!(
+            FormatSpec::parse("%3"),
+            Err(FormatSpecError::InvalidFormatSpecifier)
+        );
+        assert_eq!(
+            FormatSpec::parse(".2fa"),
+            Err(FormatSpecError::InvalidFormatSpecifier)
+        );
+        assert_eq!(
+            FormatSpec::parse("ds"),
+            Err(FormatSpecError::InvalidFormatSpecifier)
+        );
+        assert_eq!(
+            FormatSpec::parse("x+"),
+            Err(FormatSpecError::InvalidFormatSpecifier)
+        );
+        assert_eq!(
+            FormatSpec::parse("b4"),
+            Err(FormatSpecError::InvalidFormatSpecifier)
+        );
+        assert_eq!(
+            FormatSpec::parse("o!"),
+            Err(FormatSpecError::InvalidFormatSpecifier)
+        );
+        assert_eq!(
+            FormatSpec::parse("d "),
+            Err(FormatSpecError::InvalidFormatSpecifier)
+        );
+    }
+
+    #[test]
+    fn test_parse_field_name() {
+        assert_eq!(
+            FieldName::parse(""),
+            Ok(FieldName {
+                field_type: FieldType::Auto,
+                parts: Vec::new(),
+            })
+        );
+        assert_eq!(
+            FieldName::parse("0"),
+            Ok(FieldName {
+                field_type: FieldType::Index(0),
+                parts: Vec::new(),
+            })
+        );
+        assert_eq!(
+            FieldName::parse("key"),
+            Ok(FieldName {
+                field_type: FieldType::Keyword("key".to_owned()),
+                parts: Vec::new(),
+            })
+        );
+        assert_eq!(
+            FieldName::parse("key.attr[0][string]"),
+            Ok(FieldName {
+                field_type: FieldType::Keyword("key".to_owned()),
+                parts: vec![
+                    FieldNamePart::Attribute("attr".to_owned()),
+                    FieldNamePart::Index(0),
+                    FieldNamePart::StringIndex("string".to_owned())
+                ],
+            })
+        );
+        assert_eq!(
+            FieldName::parse("key.."),
+            Err(FormatParseError::EmptyAttribute)
+        );
+        assert_eq!(
+            FieldName::parse("key[]"),
+            Err(FormatParseError::EmptyAttribute)
+        );
+        assert_eq!(
+            FieldName::parse("key["),
+            Err(FormatParseError::MissingRightBracket)
+        );
+        assert_eq!(
+            FieldName::parse("key[0]after"),
+            Err(FormatParseError::InvalidCharacterAfterRightBracket)
+        );
+    }
+}
diff --git a/literal/src/lib.rs b/literal/src/lib.rs
index 9b96205..31b0f90 100644
--- a/literal/src/lib.rs
+++ b/literal/src/lib.rs
@@ -1,3 +1,4 @@
+pub mod cformat;
 pub mod char;
 pub mod escape;
 pub mod float;