Add requires-python to uv init

crates/uv-cli/src/lib.rs

@@ -1797,6 +1797,20 @@ pub struct InitArgs {
     /// Do not create a readme file.
     #[arg(long)]
     pub no_readme: bool,
+
+    /// The Python interpreter to use to determine the minimum supported Python version.
+    ///
+    /// By default, uv uses the virtual environment in the current working directory or any parent
+    /// directory, falling back to searching for a Python executable in `PATH`. The `--python`
+    /// option allows you to specify a different interpreter.
+    ///
+    /// Supported formats:
+    /// - `3.10` looks for an installed Python 3.10 using `py --list-paths` on Windows, or
+    ///   `python3.10` on Linux and macOS.
+    /// - `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.
+    #[arg(long, short, env = "UV_PYTHON", verbatim_doc_comment)]
+    pub python: Option<String>,
 }
 
 #[derive(Args)]

crates/uv-resolver/src/requires_python.rs

@@ -49,6 +49,21 @@ impl RequiresPython {
         }
     }
 
+    /// Returns a [`RequiresPython`] from a version specifier.
+    pub fn from_specifiers(specifiers: &VersionSpecifiers) -> Result<Self, RequiresPythonError> {
+        let bound = RequiresPythonBound(
+            crate::pubgrub::PubGrubSpecifier::from_release_specifiers(specifiers)?
+                .iter()
+                .next()
+                .map(|(lower, _)| lower.clone())
+                .unwrap_or(Bound::Unbounded),
+        );
+        Ok(Self {
+            specifiers: specifiers.clone(),
+            bound,
+        })
+    }
+
     /// Returns a [`RequiresPython`] to express the union of the given version specifiers.
     ///
     /// For example, given `>=3.8` and `>=3.9`, this would return `>=3.8`.

crates/uv/src/commands/project/init.rs

@@ -3,14 +3,23 @@ use std::path::PathBuf;
 
 use anyhow::Result;
 use owo_colors::OwoColorize;
-
+use pep440_rs::Version;
 use pep508_rs::PackageName;
+use uv_cache::Cache;
+use uv_client::{BaseClientBuilder, Connectivity};
 use uv_configuration::PreviewMode;
 use uv_fs::{absolutize_path, Simplified};
+use uv_python::{
+    EnvironmentPreference, PythonFetch, PythonInstallation, PythonPreference, PythonRequest,
+    VersionRequest,
+};
+use uv_resolver::RequiresPython;
 use uv_warnings::warn_user_once;
 use uv_workspace::pyproject_mut::PyProjectTomlMut;
 use uv_workspace::{Workspace, WorkspaceError};
 
+use crate::commands::project::find_requires_python;
+use crate::commands::reporters::PythonDownloadReporter;
 use crate::commands::ExitStatus;
 use crate::printer::Printer;
 
@@ -20,8 +29,14 @@ pub(crate) async fn init(
     explicit_path: Option<String>,
     name: Option<PackageName>,
     no_readme: bool,
+    python: Option<String>,
     isolated: bool,
     preview: PreviewMode,
+    python_preference: PythonPreference,
+    python_fetch: PythonFetch,
+    connectivity: Connectivity,
+    native_tls: bool,
+    cache: &Cache,
     printer: Printer,
 ) -> Result<ExitStatus> {
     if preview.is_disabled() {
@@ -62,20 +77,15 @@ pub(crate) async fn init(
     // Canonicalize the path to the project.
     let path = absolutize_path(&path)?;
 
-    // Create the `pyproject.toml`.
+    // Create the `pyproject.toml` before workspace discovery. If the directory already exists,
+    // and is a workspace member via `tools.uv.workspace`, we don't want discovery to fail due to
+    // the missing `pyproject.toml`.
     let pyproject = indoc::formatdoc! {r#"
         [project]
         name = "{name}"
         version = "0.1.0"
-        description = "Add your description here"{readme}
-        dependencies = []
-
-        [tool.uv]
-        dev-dependencies = []
         "#,
-        readme = if no_readme { "" } else { "\nreadme = \"README.md\"" },
     };
-
     fs_err::create_dir_all(&path)?;
     fs_err::write(path.join("pyproject.toml"), pyproject)?;
 
@@ -92,6 +102,90 @@ pub(crate) async fn init(
         }
     };
 
+    // Add a `requires-python` field to the `pyproject.toml`.
+    let requires_python = if let Some(request) = python.as_deref() {
+        // (1) Explicit request from user
+        match PythonRequest::parse(request) {
+            PythonRequest::Version(VersionRequest::MajorMinor(major, minor)) => {
+                RequiresPython::greater_than_equal_version(&Version::new([
+                    major as u64,
+                    minor as u64,
+                ]))
+            }
+            PythonRequest::Version(VersionRequest::MajorMinorPatch(major, minor, patch)) => {
+                RequiresPython::greater_than_equal_version(&Version::new([
+                    major as u64,
+                    minor as u64,
+                    patch as u64,
+                ]))
+            }
+            PythonRequest::Version(VersionRequest::Range(specifiers)) => {
+                RequiresPython::from_specifiers(&specifiers)?
+            }
+            request => {
+                let reporter = PythonDownloadReporter::single(printer);
+                let client_builder = BaseClientBuilder::new()
+                    .connectivity(connectivity)
+                    .native_tls(native_tls);
+                let interpreter = PythonInstallation::find_or_fetch(
+                    Some(request),
+                    EnvironmentPreference::Any,
+                    python_preference,
+                    python_fetch,
+                    &client_builder,
+                    cache,
+                    Some(&reporter),
+                )
+                .await?
+                .into_interpreter();
+                RequiresPython::greater_than_equal_version(&interpreter.python_minor_version())
+            }
+        }
+    } else if let Some(requires_python) = workspace
+        .as_ref()
+        .and_then(|workspace| find_requires_python(workspace).ok().flatten())
+    {
+        // (2) `Requires-Python` from the workspace
+        requires_python
+    } else {
+        // (3) Default to the system Python
+        let request = PythonRequest::Any;
+        let reporter = PythonDownloadReporter::single(printer);
+        let client_builder = BaseClientBuilder::new()
+            .connectivity(connectivity)
+            .native_tls(native_tls);
+        let interpreter = PythonInstallation::find_or_fetch(
+            Some(request),
+            EnvironmentPreference::Any,
+            python_preference,
+            python_fetch,
+            &client_builder,
+            cache,
+            Some(&reporter),
+        )
+        .await?
+        .into_interpreter();
+        RequiresPython::greater_than_equal_version(&interpreter.python_minor_version())
+    };
+
+    // Add the remaining metadata to the `pyproject.toml`.
+    let pyproject = indoc::formatdoc! {r#"
+        [project]
+        name = "{name}"
+        version = "0.1.0"
+        description = "Add your description here"{readme}
+        requires-python = "{requires_python}"
+        dependencies = []
+
+        [tool.uv]
+        dev-dependencies = []
+        "#,
+        readme = if no_readme { "" } else { "\nreadme = \"README.md\"" },
+        requires_python = requires_python.specifiers(),
+    };
+    fs_err::create_dir_all(&path)?;
+    fs_err::write(path.join("pyproject.toml"), pyproject)?;
+
     // Create `src/{name}/__init__.py` if it does not already exist.
     let src_dir = path.join("src").join(&*name.as_dist_info_name());
     let init_py = src_dir.join("__init__.py");

crates/uv/src/lib.rs

@@ -834,8 +834,14 @@ async fn run_project(
                 args.path,
                 args.name,
                 args.no_readme,
+                args.python,
                 globals.isolated,
                 globals.preview,
+                globals.python_preference,
+                globals.python_fetch,
+                globals.connectivity,
+                globals.native_tls,
+                &cache,
                 printer,
             )
             .await

crates/uv/src/settings.rs

@@ -154,6 +154,7 @@ pub(crate) struct InitSettings {
     pub(crate) path: Option<String>,
     pub(crate) name: Option<PackageName>,
     pub(crate) no_readme: bool,
+    pub(crate) python: Option<String>,
 }
 
 impl InitSettings {
@@ -164,12 +165,14 @@ impl InitSettings {
             path,
             name,
             no_readme,
+            python,
         } = args;
 
         Self {
             path,
             name,
             no_readme,
+            python,
         }
     }
 }