Using python argparse module for arguments starting with hyphen

Question

I am using Python 2.7. I am writing a script that uses argparse module for parsing command line arguments. The issue is there is an option -t, --tdiff that takes in time difference specified as +/-HH:MM:SS.

I coded the same as following, say in file myprog.py:

parser.add_argument("-t", "--tdiff",
                    action="store",
                    dest="time_diff",
                    help = "Specify time difference as +/-HH:MM:SS.")

Now I can run the program like "./myprog.py -t +02:30:00" but not as "./myprog.py -t -02:30:00".

Running the prog with time difference with leading hyphen prints the usage. Please help how can I circumvent this.

You can use a different prefix . . . docs.python.org/3/library/argparse.html#prefix-chars — mgilson
– mgilson, Commented Jan 13, 2016 at 4:59

FMc · Accepted Answer · 2016-01-13 05:23:28Z

3

I dislike changing the option prefix to something non-standard. Here are two approaches that I've used to handle option values that begin with a hyphen.

# Use a different symbol for negative times.
--tdiff ~02:30:00

# Use this syntax on the command line.
--tdiff=-02:30:00

answered Jan 13, 2016 at 5:23

FMc

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3 Comments

mgilson Over a year ago

+1 for the --tdiff=-XX:XX:XX option. That's what I would do too (I'm not a fan of changing the prefix-chars either).

Subhajit Kundu Over a year ago

Yup I checked. And it works without meddling with prefix_chars. Following usage works: -t=-02:30:00 or -t="-02:30:00" or -t-02:30:00. Following doesn't work: -t -02:30:00 or -t "-02:30:00".

Subhajit Kundu Over a year ago

I will accept this answer as this is closes to what I needed.

Mario Chapa · Accepted Answer · 2016-01-13 05:09:18Z

0

That - prefix is being parsed as an option, you can try to workaround this by changing the prefix used for options with prefix_chars Check out the example they give in the linked page.

edited Jan 13, 2016 at 5:09

answered Jan 13, 2016 at 4:55

Mario Chapa

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1 Comment

Mario Chapa Over a year ago

You are totally right, quotes won't fix it. Did some search in the docs and found a correct workaround by using prefix_chars.

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