#2248 Interactive interpreter hangs if pex called with a python cli option Issue created by gauthamnair Issue description and reproduction steps A pex that has no pre-defined entry point or console script is expected to open up an interactive interpreter if it isn't passed a script, module, or command as an argument:

~/code/pantsbuild/pex (main) $ python -m pex -o testpex.pex
~/code/pantsbuild/pex (main) $ ./testpex.pex
Python 3.9.17 (main, Aug  8 2023, 12:13:14) 
[Clang 14.0.3 (clang-1403.0.22.14.1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> print('hello')
hello
>>> quit()
~/code/pantsbuild/pex (main) $

If we pass a python command line option like

-q

, which normally quiets the repl preamble, the pex command hangs indefinitely:

~/code/pantsbuild/pex (main) $ python -q
>>> quit()
~/code/pantsbuild/pex (main) $ ./testpex.pex -q
# hangs ... and requires Ctrl-C

Motivation This came up while testing a fix to address pantsbuild/pants#3423 so we can pass through args to

pants repl

for the python shell. For a python shell, pants runs a

requirements.pex

as an interactive process to give a repl to the user. Usually if you want to pass args to a python repl it is going to be either interpreter options like these or it will be

-i

to run a script/module in interactive mode. Diagnosis Under the hood it hangs because pex gets into an infinite loop of re-executing itself with the same argument. We deal with python options inside `Pex.execute_interpreter`:

args = sys.argv[1:]
python_options = []
for index, arg in enumerate(args):
    # Check if the arg is an expected startup arg.
    if arg.startswith("-") and arg not in ("-", "-c", "-m"):
        python_options.append(arg)
    else:
        args = args[index:]
        break

# The pex was called with Python interpreter options
if python_options:
    return self.execute_with_options(python_options, args)

The first block of code is attempting to partition the input args into python options like

-q

or

-B

and a remainder of command line args that should be passed through when we

execute_with_options

. But when the args supplied are only python options, we do not set

args = []

because the

args = args[index:]

does not get triggered. Therefore we end up execing something like this:

# cmdline
['<path_to_python>/python3.9', '-q', '<path_to_unzipped_pex>/__main__.py', '-q']

later in

os.execv(python, cmdline)

within

execute_with_options

which puts us in an infinite loop because the pex will encounter the

-q

again as a python option. This is simple to fix, a PR will be forthcoming. pantsbuild/pex