[issue27991] In the argparse howto there is a misleading sentence about store_true

[py.user]

New submission from py.user:

https://docs.python.org/3/howto/argparse.html#combining-positional-and-optional-arguments
"And, just like the “store_true” action, if you don’t specify the -v flag, that flag is considered to have None value."

This sentence is misleading. It supposes that "store_true" action can save None value. But "store_true" action always saves True or False value.

An example:

This code was taken from the argparse howto. I've just added the -f option and printed args to the stdout.

a.py

#!/usr/bin/env python3

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("square", type=int,
                    help="display the square of a given number")
parser.add_argument("-v", "--verbosity", action="count",
                    help="increase output verbosity")
parser.add_argument("-f", "--flag", action="store_true")
args = parser.parse_args()

print('args:', args)


The output in the console:

[guest at localhost bugs]$ ./a.py 1
args: Namespace(flag=False, square=1, verbosity=None)
[guest at localhost bugs]$ 


In the output we see that the -f option have got the False value not None.

Applied a patch to the issue that just removes words about analogy with store_true action.

----------
assignee: docs at python
components: Documentation, Library (Lib)
files: argparse_store_true.diff
keywords: patch
messages: 274725
nosy: docs at python, py.user
priority: normal
severity: normal
status: open
title: In the argparse howto there is a misleading sentence about store_true
type: behavior
versions: Python 3.6
Added file: http://bugs.python.org/file44419/argparse_store_true.diff

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27991>
_______________________________________