pipx install: emit a warning when --force and --python were passed at the same time

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## dev
 
+- `pipx install`: emit a warning when `--force` and `--python` were passed at the same time
 - Drop support for Python 3.7
 - Make usage message in `pipx run` show `package_or_url`, so extra will be printed out as well
 - Add `--force-reinstall` to pip arguments when `--force` was passed

src/pipx/commands/install.py

@@ -4,6 +4,7 @@
 from pipx import constants
 from pipx.commands.common import package_name_from_spec, run_post_install_actions
 from pipx.constants import EXIT_CODE_INSTALL_VENV_EXISTS, EXIT_CODE_OK, ExitCode
+from pipx.interpreter import DEFAULT_PYTHON
 from pipx.util import pipx_wrap
 from pipx.venv import Venv, VenvContainer
 
@@ -13,19 +14,23 @@ def install(
     package_name: Optional[str],
     package_spec: str,
     local_bin_dir: Path,
-    python: str,
+    python: Optional[str],
     pip_args: List[str],
     venv_args: List[str],
     verbose: bool,
     *,
     force: bool,
+    reinstall: bool,
     include_dependencies: bool,
     preinstall_packages: Optional[List[str]],
     suffix: str = "",
 ) -> ExitCode:
     """Returns pipx exit code."""
     # package_spec is anything pip-installable, including package_name, vcs spec,
     #   zip file, or tar.gz file.
+    python_flag_was_passed = python is not None
+
+    python = python or DEFAULT_PYTHON
 
     if package_name is None:
         package_name = package_name_from_spec(
@@ -42,6 +47,16 @@ def install(
 
     venv = Venv(venv_dir, python=python, verbose=verbose)
     if exists:
+        if not reinstall and force and python_flag_was_passed:
+            print(
+                pipx_wrap(
+                    f"""
+                    --python is ignored when --force is passed.
+                    If you want to reinstall {package_name} with {python},
+                    run `pipx reinstall {package_spec} --python {python}` instead.
+                    """
+                )
+            )
         if force:
             print(f"Installing to existing venv {venv.name!r}")
             pip_args += ["--force-reinstall"]

src/pipx/commands/reinstall.py

@@ -69,6 +69,7 @@ def reinstall(
         venv.pipx_metadata.venv_args,
         verbose,
         force=True,
+        reinstall=True,
         include_dependencies=venv.pipx_metadata.main_package.include_dependencies,
         preinstall_packages=[],
         suffix=venv.pipx_metadata.main_package.suffix,

src/pipx/main.py

@@ -212,6 +212,7 @@ def run_pipx_command(args: argparse.Namespace) -> ExitCode:  # noqa: C901
             venv_args,
             verbose,
             force=args.force,
+            reinstall=False,
             include_dependencies=args.include_deps,
             preinstall_packages=args.preinstall,
             suffix=args.suffix,
@@ -344,7 +345,7 @@ def _add_install(subparsers: argparse._SubParsersAction) -> None:
     )
     p.add_argument(
         "--python",
-        default=DEFAULT_PYTHON,
+        # Don't pass a default Python here so we know whether --python flag was passed
         help=(
             "Python to install with. Possible values can be the executable name (python3.11), "
             "the version to pass to py launcher (3.11), or the full path to the executable."

tests/test_install.py

@@ -284,3 +284,14 @@ def test_preinstall(pipx_temp_env, caplog):
 def test_do_not_wait_for_input(pipx_temp_env, pipx_session_shared_dir, monkeypatch):
     monkeypatch.setenv("PIP_INDEX_URL", "http://127.0.0.1:8080/simple")
     run_pipx_cli(["install", "pycowsay"])
+
+
+def test_passed_python_and_force_flag_warning(pipx_temp_env, capsys):
+    assert not run_pipx_cli(["install", "black"])
+    assert not run_pipx_cli(["install", "--python", sys.executable, "--force", "black"])
+    captured = capsys.readouterr()
+    assert "--python is ignored when --force is passed." in captured.out
+
+    assert not run_pipx_cli(["install", "pycowsay", "--force"])
+    captured = capsys.readouterr()
+    assert "--python is ignored when --force is passed." not in captured.out