Enable freeze and list to introspect non-virtualenv Pythons (#2033)

## Summary

Now that we have the ability to introspect the installed packages for
arbitrary Pythons, we can allow `pip freeze` and `pip list` to fall back
to the "default" Python, if no virtualenv is present.

Closes https://github.com/astral-sh/uv/issues/2005.

crates/uv-interpreter/src/python_query.rs

@@ -68,7 +68,7 @@ pub fn find_requested_python(
     }
 }
 
-/// Pick a sensible default for the python a user wants when they didn't specify a version.
+/// Pick a sensible default for the Python a user wants when they didn't specify a version.
 ///
 /// We prefer the test overwrite `UV_TEST_PYTHON_PATH` if it is set, otherwise `python3`/`python` or
 /// `python.exe` respectively.

crates/uv-interpreter/src/virtual_env.rs

@@ -9,7 +9,7 @@ use uv_fs::{LockedFile, Normalized};
 
 use crate::cfg::PyVenvConfiguration;
 use crate::python_platform::PythonPlatform;
-use crate::{find_requested_python, Error, Interpreter};
+use crate::{find_default_python, find_requested_python, Error, Interpreter};
 
 /// A Python executable and its associated platform markers.
 #[derive(Debug, Clone)]
@@ -65,6 +65,15 @@ impl Virtualenv {
         })
     }
 
+    /// Create a [`Virtualenv`] for the default Python interpreter.
+    pub fn from_default_python(platform: &Platform, cache: &Cache) -> Result<Self, Error> {
+        let interpreter = find_default_python(platform, cache)?;
+        Ok(Self {
+            root: interpreter.base_prefix().to_path_buf(),
+            interpreter,
+        })
+    }
+
     /// Returns the location of the Python interpreter.
     pub fn root(&self) -> &Path {
         &self.root

crates/uv/src/commands/cache_clean.rs

@@ -12,8 +12,8 @@ use crate::printer::Printer;
 
 /// Clear the cache.
 pub(crate) fn cache_clean(
-    cache: &Cache,
     packages: &[PackageName],
+    cache: &Cache,
     mut printer: Printer,
 ) -> Result<ExitStatus> {
     if !cache.root().exists() {

crates/uv/src/commands/pip_freeze.rs

@@ -17,10 +17,25 @@ use crate::commands::ExitStatus;
 use crate::printer::Printer;
 
 /// Enumerate the installed packages in the current environment.
-pub(crate) fn pip_freeze(cache: &Cache, strict: bool, mut printer: Printer) -> Result<ExitStatus> {
+pub(crate) fn pip_freeze(
+    strict: bool,
+    python: Option<&str>,
+    cache: &Cache,
+    mut printer: Printer,
+) -> Result<ExitStatus> {
     // Detect the current Python interpreter.
     let platform = Platform::current()?;
-    let venv = Virtualenv::from_env(platform, cache)?;
+    let venv = if let Some(python) = python {
+        Virtualenv::from_requested_python(python, &platform, cache)?
+    } else {
+        match Virtualenv::from_env(platform.clone(), cache) {
+            Ok(venv) => venv,
+            Err(uv_interpreter::Error::VenvNotFound) => {
+                Virtualenv::from_default_python(&platform, cache)?
+            }
+            Err(err) => return Err(err.into()),
+        }
+    };
 
     debug!(
         "Using Python {} environment at {}",

crates/uv/src/commands/pip_list.rs

@@ -21,16 +21,27 @@ use crate::printer::Printer;
 
 /// Enumerate the installed packages in the current environment.
 pub(crate) fn pip_list(
-    cache: &Cache,
     strict: bool,
     editable: bool,
     exclude_editable: bool,
     exclude: &[PackageName],
+    python: Option<&str>,
+    cache: &Cache,
     mut printer: Printer,
 ) -> Result<ExitStatus> {
     // Detect the current Python interpreter.
     let platform = Platform::current()?;
-    let venv = Virtualenv::from_env(platform, cache)?;
+    let venv = if let Some(python) = python {
+        Virtualenv::from_requested_python(python, &platform, cache)?
+    } else {
+        match Virtualenv::from_env(platform.clone(), cache) {
+            Ok(venv) => venv,
+            Err(uv_interpreter::Error::VenvNotFound) => {
+                Virtualenv::from_default_python(&platform, cache)?
+            }
+            Err(err) => return Err(err.into()),
+        }
+    };
 
     debug!(
         "Using Python {} environment at {}",

crates/uv/src/main.rs

@@ -730,6 +730,20 @@ struct PipFreezeArgs {
     /// issues.
     #[clap(long)]
     strict: bool,
+
+    /// The Python interpreter for which packages should be listed.
+    ///
+    /// By default, `uv` lists packages in the currently activated virtual environment, or a virtual
+    /// environment (`.venv`) located in the current working directory or any parent directory,
+    /// falling back to the system Python if no virtual environment is found.
+    ///
+    /// Supported formats:
+    /// - `3.10` looks for an installed Python 3.10 using `py --list-paths` on Windows, or
+    ///   `python3.10` on Linux and macOS. (Specifying a patch version is not supported.)
+    /// - `python3.10` or `python.exe` looks for a binary with the given name in `PATH`.
+    /// - `/home/ferris/.local/bin/python3.10` uses the exact Python at the given path.
+    #[clap(long, short, verbatim_doc_comment)]
+    python: Option<String>,
 }
 
 #[derive(Args)]
@@ -751,6 +765,20 @@ struct PipListArgs {
     /// Exclude the specified package(s) from the output.
     #[clap(long)]
     r#exclude: Vec<PackageName>,
+
+    /// The Python interpreter for which packages should be listed.
+    ///
+    /// By default, `uv` lists packages in the currently activated virtual environment, or a virtual
+    /// environment (`.venv`) located in the current working directory or any parent directory,
+    /// falling back to the system Python if no virtual environment is found.
+    ///
+    /// Supported formats:
+    /// - `3.10` looks for an installed Python 3.10 using `py --list-paths` on Windows, or
+    ///   `python3.10` on Linux and macOS. (Specifying a patch version is not supported.)
+    /// - `python3.10` or `python.exe` looks for a binary with the given name in `PATH`.
+    /// - `/home/ferris/.local/bin/python3.10` uses the exact Python at the given path.
+    #[clap(long, short, verbatim_doc_comment)]
+    python: Option<String>,
 }
 
 #[derive(Args)]
@@ -1160,21 +1188,22 @@ async fn run() -> Result<ExitStatus> {
         }
         Commands::Pip(PipNamespace {
             command: PipCommand::Freeze(args),
-        }) => commands::pip_freeze(&cache, args.strict, printer),
+        }) => commands::pip_freeze(args.strict, args.python.as_deref(), &cache, printer),
         Commands::Pip(PipNamespace {
             command: PipCommand::List(args),
         }) => commands::pip_list(
-            &cache,
             args.strict,
             args.editable,
             args.exclude_editable,
             &args.exclude,
+            args.python.as_deref(),
+            &cache,
             printer,
         ),
         Commands::Cache(CacheNamespace {
             command: CacheCommand::Clean(args),
         })
-        | Commands::Clean(args) => commands::cache_clean(&cache, &args.package, printer),
+        | Commands::Clean(args) => commands::cache_clean(&args.package, &cache, printer),
         Commands::Cache(CacheNamespace {
             command: CacheCommand::Dir,
         }) => {