diff --git a/compiler/erg_common/env.rs b/compiler/erg_common/env.rs
index 59216200..5039b82b 100644
--- a/compiler/erg_common/env.rs
+++ b/compiler/erg_common/env.rs
@@ -3,24 +3,30 @@ use std::path::PathBuf;
 
 fn _erg_path() -> PathBuf {
     let path = var("ERG_PATH").unwrap_or_else(|_| env!("CARGO_ERG_PATH").to_string());
-    PathBuf::from(path).canonicalize().unwrap()
+    PathBuf::from(path)
+        .canonicalize()
+        .expect("ERG_PATH not found")
 }
 fn _erg_std_path() -> PathBuf {
-    _erg_path().join("lib").join("std").canonicalize().unwrap()
+    _erg_path()
+        .join("lib")
+        .join("std")
+        .canonicalize()
+        .expect("ERG_PATH/lib/std not found")
 }
 fn _erg_pystd_path() -> PathBuf {
     _erg_path()
         .join("lib")
         .join("pystd")
         .canonicalize()
-        .unwrap()
+        .expect("ERG_PATH/lib/pystd not found")
 }
 fn _erg_external_lib_path() -> PathBuf {
     _erg_path()
         .join("lib")
         .join("external")
         .canonicalize()
-        .unwrap()
+        .expect("ERG_PATH/lib/external not found")
 }
 
 thread_local! {
diff --git a/compiler/erg_common/error.rs b/compiler/erg_common/error.rs
index e7e34c22..a76b9d21 100644
--- a/compiler/erg_common/error.rs
+++ b/compiler/erg_common/error.rs
@@ -218,7 +218,7 @@ impl From<&str> for ErrorKind {
 }
 
 /// points the location (of an error) in a code
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
 pub enum Location {
     RangePair {
         ln_first: (usize, usize),
@@ -234,6 +234,7 @@ pub enum Location {
     },
     LineRange(usize, usize),
     Line(usize),
+    #[default]
     Unknown,
 }
 
diff --git a/compiler/erg_common/python_util.rs b/compiler/erg_common/python_util.rs
index d7bae2c2..05a43bfb 100644
--- a/compiler/erg_common/python_util.rs
+++ b/compiler/erg_common/python_util.rs
@@ -6,7 +6,7 @@ use std::process::Command;
 use crate::serialize::get_magic_num_from_bytes;
 
 #[cfg(unix)]
-pub const BUILTIN_PYTHON_MODS: [&str; 19] = [
+pub const BUILTIN_PYTHON_MODS: [&str; 20] = [
     "datetime",
     "glob",
     "http",
@@ -20,6 +20,7 @@ pub const BUILTIN_PYTHON_MODS: [&str; 19] = [
     "re",
     "shutil",
     "socket",
+    "string",
     "subprocess",
     "sys",
     "tarfile",
@@ -28,7 +29,7 @@ pub const BUILTIN_PYTHON_MODS: [&str; 19] = [
     "zipfile",
 ];
 #[cfg(not(unix))]
-pub const BUILTIN_PYTHON_MODS: [&str; 18] = [
+pub const BUILTIN_PYTHON_MODS: [&str; 19] = [
     "datetime",
     "glob",
     "http",
@@ -41,6 +42,7 @@ pub const BUILTIN_PYTHON_MODS: [&str; 18] = [
     "re",
     "shutil",
     "socket",
+    "string",
     "subprocess",
     "sys",
     "tarfile",
diff --git a/compiler/erg_compiler/lib/pystd/string.d.er b/compiler/erg_compiler/lib/pystd/string.d.er
new file mode 100644
index 00000000..05f4b860
--- /dev/null
+++ b/compiler/erg_compiler/lib/pystd/string.d.er
@@ -0,0 +1,10 @@
+.ascii_letters: Str
+.ascii_lowercase: Str
+.ascii_uppercase: Str
+.digits: Str
+.hexdigits: Str
+.octdigits: Str
+.punctuation: Str
+.printable: Str
+.whitespace: Str
+.Formatter: ClassType
diff --git a/compiler/erg_parser/parse.rs b/compiler/erg_parser/parse.rs
index 454254ce..938febb1 100644
--- a/compiler/erg_parser/parse.rs
+++ b/compiler/erg_parser/parse.rs
@@ -148,7 +148,7 @@ impl Parser {
     }
 
     fn skip_and_throw_syntax_err(&mut self, caused_by: &str) -> ParseError {
-        let loc = self.peek().unwrap().loc();
+        let loc = self.peek().map(|t| t.loc()).unwrap_or_default();
         log!(err "error caused by: {caused_by}");
         self.next_expr();
         ParseError::simple_syntax_error(0, loc)
@@ -233,7 +233,7 @@ impl Parser {
             }
         };
         if !self.cur_is(EOF) {
-            let loc = self.peek().unwrap().loc();
+            let loc = self.peek().map(|t| t.loc()).unwrap_or_default();
             self.errs
                 .push(ParseError::compiler_bug(0, loc, fn_name!(), line!()));
             return Err(mem::take(&mut self.errs));