Feature Request: Error out when -p has a path that does not point to a valid python

[rcuza]

When creating a pex, I used -p /Users/myacct/.pyenv/shims/python on the command line. This resulted in __main__.py contain BASH commands. It would be great if the pex command validated that paths passed via -p pointed to valid python interpreters.

pex -r /tmp/jupyterlab-requirements.txt -o jupyter-labs.pex -p /Users/myacct/.pyenv/shims/python built a pex that showed the following error when jupyter-labs.pex -e jupyterlab.labapp:main was run:

jupyter-labs.pex -e jupyterlab.labapp:main
Traceback (most recent call last):
  File "/Users/myacct/.pyenv/versions/3.6.9/lib/python3.6/runpy.py", line 185, in _run_module_as_main
    mod_name, mod_spec, code = _get_main_module_details(_Error)
  File "/Users/myacct/.pyenv/versions/3.6.9/lib/python3.6/runpy.py", line 219, in _get_main_module_details
    return _get_module_details(main_name)
  File "/Users/myacct/.pyenv/versions/3.6.9/lib/python3.6/runpy.py", line 128, in _get_module_details
    spec = importlib.util.find_spec(mod_name)
  File "/Users/myacct/.pyenv/versions/3.6.9/lib/python3.6/importlib/util.py", line 91, in find_spec
    return _find_spec(fullname, None)
  File "<frozen importlib._bootstrap>", line 894, in _find_spec
  File "<frozen importlib._bootstrap_external>", line 1157, in find_spec
  File "<frozen importlib._bootstrap_external>", line 1131, in _get_spec
  File "<frozen importlib._bootstrap_external>", line 1112, in _legacy_get_spec
  File "<frozen importlib._bootstrap>", line 441, in spec_from_loader
  File "<frozen importlib._bootstrap_external>", line 544, in spec_from_file_location
  File "/Users/myacct/dev/virtualenvs/tmp-bc02eb6e921a2fd/jupyter-labs.pex/__main__.py", line 3
    [ -n "$PYENV_DEBUG" ] && set -x
                      ^
SyntaxError: invalid syntax

[jsirois]

The -p flag does not mean --python it means --preamble-file. Pex just did what you asked there:

$ python -mpex -h
Usage: __main__.py [-o OUTPUT.PEX] [options] [-- arg1 arg2 ...]

__main__.py builds a PEX (Python Executable) file based on the given specifications: sources, requirements, their dependencies and other options.

Options:
  --version             show program's version number and exit
  -h, --help            show this help message and exit
  -o PEX_NAME, --output-file=PEX_NAME
                        The name of the generated .pex file: Omitting this
                        will run PEX immediately and not save it to a file.
  -p FILE, --preamble-file=FILE
                        The name of a file to be included as the preamble for
                        the generated .pex file
...

[jsirois]

I'm going to close this as answered.

[jsirois]

For posterity, the -p/--preamble-file feature implementation and example tests are in #400.

[rcuza]

Thank you and sorry for not reading!