Respect .python-version files and pyproject.toml in uv python find

Author: zanieb

crates/uv-cli/src/lib.rs

@@ -3031,6 +3031,13 @@ pub struct PythonFindArgs {
     ///
     /// See `uv help python` to view supported request formats.
     pub request: Option<String>,
+
+    /// Avoid discovering a project or workspace.
+    ///
+    /// Otherwise, when no request is provided, the Python requirement of a project in the current
+    /// directory or parent directories will be used.
+    #[arg(long, alias = "no_workspace")]
+    pub no_project: bool,
 }
 
 #[derive(Args)]

crates/uv/src/commands/python/find.rs

@@ -2,23 +2,60 @@ use anstream::println;
 use anyhow::Result;
 
 use uv_cache::Cache;
-use uv_fs::Simplified;
-use uv_python::{EnvironmentPreference, PythonInstallation, PythonPreference, PythonRequest};
+use uv_fs::{Simplified, CWD};
+use uv_python::{
+    EnvironmentPreference, PythonInstallation, PythonPreference, PythonRequest, PythonVersionFile,
+    VersionRequest,
+};
+use uv_resolver::RequiresPython;
+use uv_warnings::warn_user_once;
+use uv_workspace::{DiscoveryOptions, VirtualProject, WorkspaceError};
 
-use crate::commands::ExitStatus;
+use crate::commands::{project::find_requires_python, ExitStatus};
 
 /// Find a Python interpreter.
 pub(crate) async fn find(
     request: Option<String>,
+    no_project: bool,
+    no_config: bool,
     python_preference: PythonPreference,
     cache: &Cache,
 ) -> Result<ExitStatus> {
-    let request = match request {
-        Some(request) => PythonRequest::parse(&request),
-        None => PythonRequest::Any,
-    };
+    // (1) Explicit request from user
+    let mut request = request.map(|request| PythonRequest::parse(&request));
+
+    // (2) Request from `.python-version`
+    if request.is_none() {
+        request = PythonVersionFile::discover(&*CWD, no_config)
+            .await?
+            .and_then(PythonVersionFile::into_version);
+    }
+
+    // (3) `Requires-Python` in `pyproject.toml`
+    if request.is_none() && !no_project {
+        let project = match VirtualProject::discover(&CWD, &DiscoveryOptions::default()).await {
+            Ok(project) => Some(project),
+            Err(WorkspaceError::MissingProject(_)) => None,
+            Err(WorkspaceError::MissingPyprojectToml) => None,
+            Err(WorkspaceError::NonWorkspace(_)) => None,
+            Err(err) => {
+                warn_user_once!("{err}");
+                None
+            }
+        };
+
+        if let Some(project) = project {
+            request = find_requires_python(project.workspace())?
+                .as_ref()
+                .map(RequiresPython::specifiers)
+                .map(|specifiers| {
+                    PythonRequest::Version(VersionRequest::Range(specifiers.clone()))
+                });
+        }
+    }
+
     let python = PythonInstallation::find(
-        &request,
+        &request.unwrap_or_default(),
         EnvironmentPreference::OnlySystem,
         python_preference,
         cache,

crates/uv/src/lib.rs

@@ -916,7 +916,14 @@ async fn run(cli: Cli) -> Result<ExitStatus> {
             // Initialize the cache.
             let cache = cache.init()?;
 
-            commands::python_find(args.request, globals.python_preference, &cache).await
+            commands::python_find(
+                args.request,
+                args.no_project,
+                cli.no_config,
+                globals.python_preference,
+                &cache,
+            )
+            .await
         }
         Commands::Python(PythonNamespace {
             command: PythonCommand::Pin(args),

crates/uv/src/settings.rs

@@ -564,15 +564,22 @@ impl PythonUninstallSettings {
 #[derive(Debug, Clone)]
 pub(crate) struct PythonFindSettings {
     pub(crate) request: Option<String>,
+    pub(crate) no_project: bool,
 }
 
 impl PythonFindSettings {
     /// Resolve the [`PythonFindSettings`] from the CLI and workspace configuration.
     #[allow(clippy::needless_pass_by_value)]
     pub(crate) fn resolve(args: PythonFindArgs, _filesystem: Option<FilesystemOptions>) -> Self {
-        let PythonFindArgs { request } = args;
+        let PythonFindArgs {
+            request,
+            no_project,
+        } = args;
 
-        Self { request }
+        Self {
+            request,
+            no_project,
+        }
     }
 }
 

crates/uv/tests/python_find.rs

@@ -1,5 +1,9 @@
 #![cfg(all(feature = "python", feature = "pypi"))]
 
+use assert_fs::fixture::FileWriteStr;
+use assert_fs::prelude::PathChild;
+use indoc::indoc;
+
 use common::{uv_snapshot, TestContext};
 use uv_python::platform::{Arch, Os};
 
@@ -148,3 +152,94 @@ fn python_find() {
     ----- stderr -----
     "###);
 }
+
+#[test]
+fn python_find_pin() {
+    let context: TestContext = TestContext::new_with_versions(&["3.11", "3.12"]);
+
+    // Pin to a version
+    uv_snapshot!(context.filters(), context.python_pin().arg("3.12"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Pinned `.python-version` to `3.12`
+
+    ----- stderr -----
+    "###);
+
+    // We should find the pinned version, not the first on the path
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.12]
+
+    ----- stderr -----
+    "###);
+
+    // Unless explictly requested
+    uv_snapshot!(context.filters(), context.python_find().arg("3.11"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    "###);
+
+    // Or `--no-config` is used
+    uv_snapshot!(context.filters(), context.python_find().arg("--no-config"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    "###);
+}
+
+#[test]
+fn python_find_project() {
+    let context: TestContext = TestContext::new_with_versions(&["3.11", "3.12"]);
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml
+        .write_str(indoc! {r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["anyio==3.7.0"]
+    "#})
+        .unwrap();
+
+    // We should respect the project's required version, not the first on the path
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.12]
+
+    ----- stderr -----
+    "###);
+
+    // Unless explictly requested
+    uv_snapshot!(context.filters(), context.python_find().arg("3.11"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    "###);
+
+    // Or `--no-project` is used
+    uv_snapshot!(context.filters(), context.python_find().arg("--no-project"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    "###);
+}