New submission from Ryan Govostes <[email protected]>:
argparse supports consuming multiple command-line arguments with nargs=2, etc.
It converts them to the type given in the argument's type parameter.
argparse does not provide a good solution when the input arguments should be
different data types. For an example, you cannot have an argument that expects
a str followed by an int, '--set-age Bob 34'.
Ordinarily, the suggestion would be to split it into two arguments, like
'--set-person Bob --set-age 34'.
However, this becomes awkward with an action such as 'append', where the
command line arguments become tedious, like '--set-person Bob --set-age 34
--set-person Alice --set-age 29', or confusing, as in '--set-person Bob
--set-person Alice --set-age 34 --set-age 29'.
My proposal is to allow the 'type' parameter to accept a tuple of types:
p.add_argument('--set-age', nargs=2, type=(str, int))
Since 'nargs' is redundant, this could even be simplified to just:
p.add_argument('--set-age', type=(str, int))
The resulting parsed argument would then be a tuple of (str, int), as opposed
to a list. If action='append', the result would be a list of such tuples.
This creates no backwards compatibility issue because tuple instances are not
callable, so this was never valid code that did something else.
A further enhancement could be that when nargs='+' or '*', and a tuple of types
is provided, the types are used round robin: '--set-ages Bob 34 Alice 29'. An
exception would be raised if it would create an incomplete tuple.
See here for other discussion and workarounds:
https://stackoverflow.com/questions/16959101/python-argparse-how-to-have-nargs-2-with-type-str-and-type-int
----------
components: Library (Lib)
messages: 352741
nosy: rgov
priority: normal
severity: normal
status: open
title: argparse should support multiple types when nargs > 1
type: enhancement
versions: Python 2.7, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9
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Python tracker <[email protected]>
<https://bugs.python.org/issue38217>
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