Added pyvm use <version> for session-level switching

[ParthG2209]

fixes #54

I added a new use command to the CLI that lets you temporarily switch Python versions for your current session. It works by creating a temporary environment with symlinks to the requested version and spawning a subshell, so when you exit, you are right back to your default setup. This makes testing across different versions much easier without changing global defaults.

[ParthG2209]

@shreyasmene06 kindly verify the pr

[shreyasmene06]

Thanks for tackling this feature! The subshell approach is a sensible way to implement session-level switching. However, there are several issues that need to be fixed before merging.

Required Changes

1. Wrong function: click.exit() should be sys.exit()

Throughout the code you're using click.exit(1) which doesn't exist. Click uses sys.exit() or you can raise SystemExit(1):

# ❌ Wrong (lines 625, 634, 680, 705)
click.exit(1)
# ✅ Correct
sys.exit(1)

This will cause AttributeError: module 'click' has no attribute 'exit' at runtime.
2. Inconsistent indentation
Several lines have incorrect indentation (extra space):

Lines 624-625, 628-638, 659-667, 676, 695-699

if not validate_version_string(version):
click.echo(...) # <-- 5 spaces instead of 4
click.exit(1)
Please fix to use consistent 4-space indentation throughout.
3. Missing tests
This is a significant new feature that modifies shell behavior. Please add tests for:

• Version validation
• Finding Python executable
• Symlink creation logic
• Error handling (version not found, symlink failures)
  Even if you can't easily test the subshell spawning, the setup/teardown logic can be unit tested.
  Suggestions (non-blocking)

4. Security: validate version before using in paths

   The version string is used directly in tempfile.mkdtemp(prefix=f"pyvm_session_{version}_"). While mkdtemp is safe, consider validating the version more strictly to prevent any path traversal edge cases.

5. Windows pip linking is inside the else block

   The pip symlink logic (lines 672-678) is inside the else: (non-Windows) branch, so pip won't be linked on Windows.

6. Consider using os.execvpe instead of subprocess.run

   Using subprocess.run([current_shell]) creates a child process. Using os.execvpe would replace the current process, which is more typical for shell switching tools. However, your approach works and allows for cleanup, so this is optional.

7. Add --shell option?

   Users might want to specify a different shell than their default.

[ParthG2209]

@shreyasmene06 i have made all the fixes kindly verify the files now

[ParthG2209]

@shreyasmene06 kindly merge the PR

[shreyasmene06]

All previous feedback has been addressed:

• Fixed click.exit() → sys.exit() throughout
• Fixed inconsistent indentation
• Added comprehensive tests (test_cli_use.py)
• Fixed Windows pip linking (now checks Scripts directory)
• The implementation is clean:
• Subshell approach is sensible for session-level switching
• Proper cleanup with shutil.rmtree in finally block
• Good fallback to .bat shim when Windows symlinks fail
• Tests cover Linux, Windows, invalid version, and version-not-found cases
  One minor note (non-blocking): The commented-out assertion in test_use_version_success_linux (line 39-40) could be uncommented or removed to keep tests clean, but that's trivial.
  LGTM! 🎉

[shreyasmene06]

@ParthG2209 everything is perfectly done just make sure the formatting checks are passed you can see the contribution.md there I have shared how to run the tests locally

[ParthG2209]

@shreyasmene06 i have made the changes, kindly add the acwoc and difficulty tags and merge the PR

[shreyasmene06]

@ParthG2209 I can see still the formatting checks have failed please make sure these pass

[ParthG2209]

@shreyasmene06 kindly verify the files now

[ParthG2209]

@shreyasmene06 pls verify the PR

[ParthG2209]

@shreyasmene06 kindly verify the PR

[shreyasmene06]

Everything is perfect but you just need to make sure the workflow check passes as these small things might cause a big vulnerability later...

[ParthG2209]

Everything is perfect but you just need to make sure the workflow check passes as these small things might cause a big vulnerability later...

@shreyasmene06 All tests have been cleared kindly merge the PR