argparse limitations

Oscar Benjamin oscar.j.benjamin at gmail.com
Tue Jul 31 11:55:57 CEST 2012


On Jul 31, 2012 10:32 AM, "Benoist Laurent" <benoist at ibpc.fr> wrote:
>
> Well sorry about that but it seems I was wrong.
> It was Friday evening and I guess I've not been careful.
>
> Actually when you specify nargs="?",  the doc says "One argument will be
consumed from the command line if possible, and produced as a single item".
> So you can't pass several arguments to the program.

Right below that in the docs it explains about using nargs='*' and
nargs='+'. One of those will do what you want.

Oscar.

>
> So, to rephrase the question, how can I get a argument parser that parses
the command-line just as Unix grep would do?
> i.e.
>
> $ echo 42 > foo.txt
> $ echo 172 >> foo.txt
> $ cp foo.txt bar.txt
> $
> $ grep 42 foo.txt
> 42
> $ grep 42 foo.txt bar.txt
> foo.txt:42
> bar.txt:42
> $ cat foo.txt | grep 42
> 42
> $ grep -c 42 foo.txt
> 1
>
>
> Cheers,
> Ben
>
>
>
>
> Le Jul 27, 2012 à 7:08 PM, Benoist Laurent a écrit :
>
>>
>>
>> Yes basically looks like you get it.
>> I have to further test it but my first impression is that it's correct.
>>
>> So actually the point was to use nargs="?".
>>
>> Thank you very much.
>> Ben
>>
>>
>>
>> Le Jul 27, 2012 à 5:44 PM, Peter Otten a écrit :
>>
>>> Benoist Laurent wrote:
>>>
>>>> I'm impletting a tool in Python.
>>>>
>>>> I'd like this tool to behave like a standard unix tool, as grep for
>>>>
>>>> exemple. I chose to use the argparse module to parse the command line
and
>>>>
>>>> I think I'm getting into several limitations of this module.
>>>>
>>>>
>>>>> First Question.
>>>>
>>>> How can I configure the the ArgumentParser to allow the user to give
>>>>
>>>> either an input file or to pipe the output from another program?
>>>>
>>>>
>>>> $ mytool.py file.txt
>>>>
>>>> $ cat file.txt | mytool.py
>>>
>>>
>>> $ echo alpha > in.txt
>>> $ cat in.txt | ./mytool.py
>>> ALPHA
>>> $ cat in.txt | ./mytool.py - out.txt
>>> $ cat out.txt
>>> ALPHA
>>> $ ./mytool.py in.txt
>>> ALPHA
>>> $ ./mytool.py in.txt out2.txt
>>> $ cat out2.txt
>>> ALPHA
>>> $ cat ./mytool.py
>>> #!/usr/bin/env python
>>> assert __name__ == "__main__"
>>>
>>> import argparse
>>> import sys
>>>
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument("infile", nargs="?", type=argparse.FileType("r"),
>>> default=sys.stdin)
>>> parser.add_argument("outfile", nargs="?", type=argparse.FileType("w"),
>>> default=sys.stdout)
>>> args = parser.parse_args()
>>>
>>> args.outfile.writelines(line.upper() for line in args.infile)
>>>
>>> Is that good enough?
>>>
>>>
>>> --
>>> http://mail.python.org/mailman/listinfo/python-list
>>>
>>
>> --
>> Benoist Laurent
>> Laboratoire de Biochimie Theorique / CNRS UPR 9080
>> Institut de Biologie Physico-Chimique
>> 13, rue Pierre et Marie Curie
>> F-75005 Paris
>> Tel. +33 [0]1 58 41 51 67 or +33 [0]6 21 64 50 56
>>
>> --
>> http://mail.python.org/mailman/listinfo/python-list
>
>
> --
> Benoist Laurent
> Laboratoire de Biochimie Theorique / CNRS UPR 9080
> Institut de Biologie Physico-Chimique
> 13, rue Pierre et Marie Curie
> F-75005 Paris
> Tel. +33 [0]1 58 41 51 67 or +33 [0]6 21 64 50 56
>
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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