How do I make a command line argument act as either a flag or a parsed value?

user_608558 0
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How do I specify that a parsed argument should be:

  • False if not specified
  • True if present (with no value)
  • or the specified value

For example I would like the following to happen:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("--the_arg", ...)

print(parser.parse_args(["--the_arg"]).the_arg)              # should print True
print(parser.parse_args([]).the_arg)                         # should print False
print(parser.parse_args(["--the_arg", "my_value"]).the_arg)  # should print "my_value"
argparse python
1 Answers

The solution is to specify all of the nargs, const, and default parameters of parser.add_argument

This works:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("--the_arg", nargs="?", const=True, default=False)

print(parser.parse_args(["--the_arg"]).the_arg) #prints True
print(parser.parse_args().the_arg) #prints False
print(parser.parse_args(["--the_arg", "my_value"]).the_arg) #prints "my_value"
user_6085580
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