Respect --isolated in uv python install (#4938)

We ignore Python version files when `--isolated` is used, logging that
we skipped them if they exist.

crates/uv-python/src/lib.rs

@@ -13,9 +13,11 @@ pub use crate::pointer_size::PointerSize;
 pub use crate::prefix::Prefix;
 pub use crate::python_version::PythonVersion;
 pub use crate::target::Target;
-pub use crate::version_files::{request_from_version_file, requests_from_version_file};
+pub use crate::version_files::{
+    request_from_version_file, requests_from_version_file, version_file_exists,
+    versions_file_exists, PYTHON_VERSIONS_FILENAME, PYTHON_VERSION_FILENAME,
+};
 pub use crate::virtualenv::{Error as VirtualEnvError, PyVenvConfiguration, VirtualEnvironment};
-
 mod discovery;
 pub mod downloads;
 mod environment;

crates/uv-python/src/version_files.rs

@@ -4,6 +4,12 @@ use tracing::debug;
 
 use crate::PythonRequest;
 
+/// The file name for Python version pins.
+pub static PYTHON_VERSION_FILENAME: &str = ".python-version";
+
+/// The file name for multiple Python version declarations.
+pub static PYTHON_VERSIONS_FILENAME: &str = ".python-versions";
+
 /// Read [`PythonRequest`]s from a version file, if present.
 ///
 /// Prefers `.python-versions` then `.python-version`.
@@ -41,25 +47,33 @@ pub async fn request_from_version_file() -> Result<Option<PythonRequest>, io::Er
     }
 }
 
+pub fn versions_file_exists() -> Result<bool, io::Error> {
+    PathBuf::from(PYTHON_VERSIONS_FILENAME).try_exists()
+}
+
 async fn read_versions_file() -> Result<Option<Vec<String>>, io::Error> {
-    if !PathBuf::from(".python-versions").try_exists()? {
+    if !versions_file_exists()? {
         return Ok(None);
     }
-    debug!("Reading requests from `.python-versions`");
-    let lines: Vec<String> = fs::tokio::read_to_string(".python-versions")
+    debug!("Reading requests from `{PYTHON_VERSIONS_FILENAME}`");
+    let lines: Vec<String> = fs::tokio::read_to_string(PYTHON_VERSIONS_FILENAME)
         .await?
         .lines()
         .map(ToString::to_string)
         .collect();
     Ok(Some(lines))
 }
 
+pub fn version_file_exists() -> Result<bool, io::Error> {
+    PathBuf::from(PYTHON_VERSION_FILENAME).try_exists()
+}
+
 async fn read_version_file() -> Result<Option<String>, io::Error> {
-    if !PathBuf::from(".python-version").try_exists()? {
+    if !version_file_exists()? {
         return Ok(None);
     }
-    debug!("Reading requests from `.python-version`");
-    Ok(fs::tokio::read_to_string(".python-version")
+    debug!("Reading requests from `{PYTHON_VERSION_FILENAME}`");
+    Ok(fs::tokio::read_to_string(PYTHON_VERSION_FILENAME)
         .await?
         .lines()
         .next()

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

@@ -1,18 +1,22 @@
 use std::collections::BTreeSet;
 use std::fmt::Write;
+use std::path::PathBuf;
 
 use anyhow::Result;
 use fs_err as fs;
 use futures::StreamExt;
 use itertools::Itertools;
 use owo_colors::OwoColorize;
+use tracing::debug;
 use uv_cache::Cache;
 use uv_client::Connectivity;
 use uv_configuration::PreviewMode;
 use uv_fs::Simplified;
 use uv_python::downloads::{self, DownloadResult, ManagedPythonDownload, PythonDownloadRequest};
 use uv_python::managed::{ManagedPythonInstallation, ManagedPythonInstallations};
-use uv_python::{requests_from_version_file, PythonRequest};
+use uv_python::{
+    requests_from_version_file, PythonRequest, PYTHON_VERSIONS_FILENAME, PYTHON_VERSION_FILENAME,
+};
 use uv_warnings::warn_user_once;
 
 use crate::commands::reporters::PythonDownloadReporter;
@@ -43,15 +47,17 @@ pub(crate) async fn install(
     let targets = targets.into_iter().collect::<BTreeSet<_>>();
     let requests: Vec<_> = if targets.is_empty() {
         // Read from the version file, unless `isolated` was requested
-        if let Some(requests) = if isolated {
+        let version_file_requests = if isolated {
+            if PathBuf::from(PYTHON_VERSION_FILENAME).exists() {
+                debug!("Ignoring `.python-version` file due to isolated mode");
+            } else if PathBuf::from(PYTHON_VERSIONS_FILENAME).exists() {
+                debug!("Ignoring `.python-versions` file due to isolated mode");
+            }
             None
         } else {
             requests_from_version_file().await?
-        } {
-            requests
-        } else {
-            vec![PythonRequest::Any]
-        }
+        };
+        version_file_requests.unwrap_or_else(|| vec![PythonRequest::Any])
     } else {
         targets
             .iter()

crates/uv/tests/venv.rs

@@ -3,6 +3,7 @@
 use anyhow::Result;
 use assert_cmd::prelude::*;
 use assert_fs::prelude::*;
+use uv_python::{PYTHON_VERSIONS_FILENAME, PYTHON_VERSION_FILENAME};
 
 use crate::common::{uv_snapshot, TestContext};
 
@@ -109,7 +110,7 @@ fn create_venv_reads_request_from_python_version_file() {
     // With a version file, we should prefer that version
     context
         .temp_dir
-        .child(".python-version")
+        .child(PYTHON_VERSION_FILENAME)
         .write_str("3.12")
         .unwrap();
 
@@ -150,7 +151,7 @@ fn create_venv_reads_request_from_python_versions_file() {
     // With a versions file, we should prefer the first listed version
     context
         .temp_dir
-        .child(".python-versions")
+        .child(PYTHON_VERSIONS_FILENAME)
         .write_str("3.12\n3.11")
         .unwrap();
 
@@ -176,7 +177,7 @@ fn create_venv_explicit_request_takes_priority_over_python_version_file() {
 
     context
         .temp_dir
-        .child(".python-version")
+        .child(PYTHON_VERSION_FILENAME)
         .write_str("3.12")
         .unwrap();