argparse supports short options, single-dash long options and double-dash long options. Values for option can be specified as separate argument (for all types of options):

--option value
-option value
-o value

It can also be grouped in a single argument with the option. In this case it should be separated by = from the option name:

--option=value
-option=value
-ovalue

argparse also supports abbreviation of long options (enabled by default):

--opt value
-opt value

Abbreviated double-dash long options can be used with =:

--opt=value

But this does not work with single-dash long options:

-opt=value

This is definitely an omission. There are other bugs related to abbreviation (#104860) and use with = (#124305). There were many other bugs related to this code. This code is just not well tested.

The code for --opt=value is not tested as well -- breaking it does not break tests.

Linked PRs

• gh-124345: Support abbreviated single-dash long options with = in argparse #124428
• [3.13] gh-124345: Support abbreviated single-dash long options with = in argparse (GH-124428) #124753
• [3.12] gh-124345: Support abbreviated single-dash long options with = in argparse (GH-124428) #124754