FileNotFoundError when upgrading model-checker: 'pip' command not found

[benbrastmckie]

Bug Description

The model-checker -u upgrade command fails with a FileNotFoundError because it tries to call pip directly, which doesn't exist on many systems where only pip3 is available.

Environment

• OS: macOS (Darwin 24.6.0)
• Python: 3.13
• model-checker version: 1.1.0
• Installation method: pip3 install model-checker

Steps to Reproduce

1. Install model-checker: pip3 install model-checker
2. Run: model-checker -u to upgrade

Expected Behavior

The package should upgrade successfully.

Actual Behavior

The upgrade fails with the following error:

◆ Documents ❯❯❯ model-checker -u
Upgrading package
Traceback (most recent call last):
  File "/Users/nicky/Library/Python/3.13/bin/model-checker", line 7, in <module>
    sys.exit(run())
             ~~~^^
  File "/Users/nicky/Library/Python/3.13/lib/python/site-packages/model_checker/__main__.py", line 266, in run
    main()
    ~~~~^^
  File "/Users/nicky/Library/Python/3.13/lib/python/site-packages/model_checker/__main__.py", line 244, in main
    subprocess.run(['pip', 'install', '--upgrade', package_name], check=True)
    ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Cellar/python@3.13/3.13.7/Frameworks/Python.framework/Versions/3.13/lib/python3.13/subprocess.py", line 554, in run
    with Popen(*popenargs, **kwargs) as process:
         ~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Cellar/python@3.13/3.13.7/Frameworks/Python.framework/Versions/3.13/lib/python3.13/subprocess.py", line 1039, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        pass_fds, cwd, env,
                        ^^^^^^^^^^^^^^^^^^^
    ...<5 lines>...
                        gid, gids, uid, umask,
                        ^^^^^^^^^^^^^^^^^^^^^^
                        start_new_session, process_group)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Cellar/python@3.13/3.13.7/Frameworks/Python.framework/Versions/3.13/lib/python3.13/subprocess.py", line 1972, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'pip'

Root Cause

The issue is in __main__.py line 244 which hardcodes 'pip' in the subprocess call:

subprocess.run(['pip', 'install', '--upgrade', package_name], check=True)

On many systems (especially macOS with Homebrew Python), only pip3 exists in the PATH, not pip.

Suggested Fix

The code should use one of these approaches:

1. Use sys.executable -m pip instead of calling pip directly:

   subprocess.run([sys.executable, '-m', 'pip', 'install', '--upgrade', package_name], check=True)

2. Try pip first, fall back to pip3 if not found
3. Use shutil.which() to find the available pip command

Option 1 is the most reliable as it ensures using the same Python interpreter that's running the script.

[benbrastmckie]

Update: Issue persists after pip.conf configuration

I've configured my pip.conf to bypass the externally-managed-environment restrictions, but the upgrade command still fails with the same error:

◆ Documents ❯❯❯ model-checker -u
Upgrading package
Traceback (most recent call last):
  File "/Users/nicky/Library/Python/3.13/bin/model-checker", line 7, in <module>
    sys.exit(run())
             ~~~^^
  File "/Users/nicky/Library/Python/3.13/lib/python/site-packages/model_checker/__main__.py", line 266, in run
    main()
    ~~~~^^
  File "/Users/nicky/Library/Python/3.13/lib/python/site-packages/model_checker/__main__.py", line 244, in main
    subprocess.run(['pip', 'install', '--upgrade', package_name], check=True)
    ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Cellar/python@3.13/3.13.7/Frameworks/Python.framework/Versions/3.13/lib/python3.13/subprocess.py", line 554, in run
    with Popen(*popenargs, **kwargs) as process:
         ~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Cellar/python@3.13/3.13.7/Frameworks/Python.framework/Versions/3.13/lib/python3.13/subprocess.py", line 1039, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        pass_fds, cwd, env,
                        ^^^^^^^^^^^^^^^^^^^
    ...<5 lines>...
                        gid, gids, uid, umask,
                        ^^^^^^^^^^^^^^^^^^^^^^
                        start_new_session, process_group)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Cellar/python@3.13/3.13.7/Frameworks/Python.framework/Versions/3.13/lib/python3.13/subprocess.py", line 1972, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'pip'

The root issue remains: the hardcoded 'pip' command in the subprocess call doesn't exist on my system (macOS with Homebrew Python), only pip3 is available.

Current PATH status:

• which pip: command not found
• which pip3: /usr/local/bin/pip3

This confirms that the suggested fix to use sys.executable -m pip or check for available pip commands is still needed.