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argparse: fix inconsistency in add_argument() API when using positional argument with dest= parameter #117834
Description
Feature or enhancement
Proposal:
Current behaviour is ugly and inconsistent between options and positional arguments:
parser.add_argument("--option-foo", dest="my_foo_option_var")
parser.add_argument(metavar="BAR_ARG", dest="my_bar_arg_var")
# or even worse
parser.add_argument("my_bar_arg_var", metavar="BAR_ARG")Proposed change streamlines the library API
parser.add_argument("--option-foo", dest="my_foo_option_var")
parser.add_argument("BAR_ARG", dest="my_bar_arg_var")I think a small patch could fix this without breaking any existing code.
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1423,7 +1423,7 @@
# =======================
def add_argument(self, *args, **kwargs):
"""
- add_argument(dest, ..., name=value, ...)
+ add_argument(arg, ..., name=value, ...)
add_argument(option_string, option_string, ..., name=value, ...)
"""
@@ -1433,7 +1433,11 @@
chars = self.prefix_chars
if not args or len(args) == 1 and args[0][0] not in chars:
if args and 'dest' in kwargs:
- raise ValueError('dest supplied twice for positional argument')
+ if 'metavar' not in kwargs:
+ kwargs['metavar'] = args[0]
+ else:
+ raise ValueError('`arg` supplied with both `dest` and `metavar` for positional argument')
+ args = (kwargs.pop('dest'), )
kwargs = self._get_positional_kwargs(*args, **kwargs)
# otherwise, we're adding an optional argumentHas this already been discussed elsewhere?
This is a minor feature, which does not need previous discussion elsewhere
Links to previous discussion of this feature:
No response
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