[issue28742] argparse.ArgumentDefaultsHelpFormatter sometimes provides inaccurate documentation of defaults, so they should be overrideable

[Peter Eckersley]

New submission from Peter Eckersley:

When argparse lists the default values for cli flags and arguments, it shows argparse's view of the internal Pythonic default, not the default behaviour of the program as a whole. This can be wrong in many cases, as documented at https://bugs.python.org/issue27153 and https://github.com/certbot/certbot/issues/3734.

To mitigate this, we should allow the caller to set arbitrary strings that argparse will display to the user as the "default" in the CLI help.

I wrote a first patch to do this via a new "help_default" argument that can be added to argparse actions:

https://gist.github.com/pde/daec08cadc21bca0d62852020887ee13

The patch was written against argparse.py from Python2.7, but seems to apply and run okay against the Python 3.x version.

----------
messages: 281183
nosy: pde
priority: normal
severity: normal
status: open
title: argparse.ArgumentDefaultsHelpFormatter sometimes provides inaccurate documentation of defaults, so they should be overrideable
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28742>
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