Fix Python – Using the same option multiple times in Python’s argparse


Asked By – John Allard

I’m trying to write a script that accepts multiple input sources and does something to each one. Something like this

./ \
    -i input1_url input1_name input1_other_var \
    -i input2_url input2_name input2_other_var \
    -i input3_url input3_name
# notice inputX_other_var is optional

But I can’t quite figure out how to do this using argparse. It seems that it’s set up so that each option flag can only be used once. I know how to associate multiple arguments with a single option (nargs='*' or nargs='+'), but that still won’t let me use the -i flag multiple times. How do I go about accomplishing this?

Just to be clear, what I would like in the end is a list of lists of strings. So

[["input1_url", "input1_name", "input1_other"],
 ["input2_url", "input2_name", "input2_other"],
 ["input3_url", "input3_name"]]

Now we will see solution for issue: Using the same option multiple times in Python’s argparse


Here’s a parser that handles a repeated 2 argument optional – with names defined in the metavar:


In [295]: parser.print_help()
usage: ipython2.7 [-h] [-i url name]

optional arguments:
  -h, --help            show this help message and exit
  -i url name, --input url name

In [296]: parser.parse_args('-i one two -i three four'.split())
Out[296]: Namespace(input=[['one', 'two'], ['three', 'four']])

This does not handle the 2 or 3 argument case (though I wrote a patch some time ago for a Python bug/issue that would handle such a range).

How about a separate argument definition with nargs=3 and metavar=('url','name','other')?

The tuple metavar can also be used with nargs='+' and nargs='*'; the 2 strings are used as [-u A [B ...]] or [-u [A [B ...]]].

This question is answered By – hpaulj

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