Argparse add option strings

Question

That question will be strange in some point...

I'm trying to add the option strings in the parser after adding one argument.

For example

import argparse
p = argparse.ArgumentParser()
p.add_argument(dest = 'myvar')
p._actions[1].option_strings = ['-foo']
p.parse_args('-foo 1')

This example doesn't work, it says:

: error: the following arguments are required: -foo

Even though I'm supplying the argument...

Anyone know why this is occurring?

Is there some way to add the option strings after the add_argument method?

JoshuaCS · Accepted Answer · 2018-12-13 16:04:13Z

1

After looking at the source code of argparse, I found you also have to register the action by the option string it has:

import argparse

p = argparse.ArgumentParser()
p.add_argument(dest = 'myvar')
p._actions[1].option_strings = ['-foo']

# You also need to do this
p._option_string_actions['-foo'] = p._actions[1]

args = p.parse_args(['-foo', '100'])
print('myvar is', args.myvar)  # myvar is 1

Note the change when calling parse_args.

I hope this help!!

edited Dec 13, 2018 at 16:04

answered Dec 13, 2018 at 2:32

JoshuaCS

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5 Comments

kaihami Over a year ago

I know this behaviour, and how the argparse acts using this syntax. Although my question is a little bit more complicated. I want to add the option strings after adding one argument....

JoshuaCS Over a year ago

@kaihami, the source code of argparse gave me the answer. I edited my answer above and think that is what you are looking for.

JoshuaCS Over a year ago

@kaihami The main problem is that you are trying to hack on argparse and thus, you were bypassing its registration mechanism and all the setup it does

kaihami Over a year ago

Thank you indeed I forgot about p._option_strings_actions!

JoshuaCS Over a year ago

Please, @kaihami , mark my answer as the right one if you think it helped you. I will really appreciate it. Thanks

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