Python doctest for shell scripts that test argument parsing without polluting docstring with os.popen()

Question

Is there a way to write a python doctest string to test a script intended to be launched from the command line (terminal) that doesn't pollute the documentation examples with os.popen calls?

#!/usr/bin/env python
# filename: add
"""
Example:
>>> import os
>>> os.popen('add -n 1 2').read().strip()
'3'
"""

if __name__ == '__main__':
    from argparse import ArgumentParser
    p = ArgumentParser(description=__doc__.strip())
    p.add_argument('-n',type = int, nargs   = 2, default = 0,help  = 'Numbers to add.')
    p.add_argument('--test',action = 'store_true',help  = 'Test script.')
    a = p.parse_args()
    if a.test:
        import doctest
        doctest.testmod()
    if a.n and len(a.n)==2:
        print a.n[0]+a.n[1]

Running doctest.testmod() without using popen just causes a test failure because the script is run within a python shell instead of a bash (or DOS) shell.

The advanced python course at LLNL suggests putting scripts in files that are separate from .py modules. But then the doctest strings only test the module, without the arg parsing. And my os.popen() approach pollutes the Examples documentation. Is there a better way?

Answer 1

Just found something looking like the answer you want: shell-doctest.

Answer 2

doctest is meant to run python code, so you have to do a conversion somewhere. If you are determined to test the commandline interface directly via doctest, one possibility is to do a regexp substitution to __doc__ before you pass it to argparse, to take out the os.popen wrapper:

clean = re.sub(r"^>>> os\.popen\('(.*)'\).*", r"% \1", __doc__)
p = ArgumentParser(description=clean, ...)

(Of course there are all sorts of nicer ways to do that, depending on what you consider "nice").

That'll clean it up for the end user. If you also want it to look cleaner in the source, you can go the other way: Put commandline examples in the docstring and don't use doctest.testmodule(). Run your docstring through doctest.script_from_examples and post-process it to insert the os calls. (Then you'll have to embed it into something so you can test it with run_docstring_examples.) doctest doesn't care if the input is valid python, so you can do the following:

>>> print doctest.script_from_examples("""
Here is a commandline example I want converted:
>>> add -n 3 4
7
""")
# Here is a commandline example I want converted:
add -n 3 4
# Expected:
## 7

This will still expose the python prompt >>> in the help. If this bothers you, you may just have to process the string in both directions.