argparse.ArgumentParser("blah")

[Roy Smith]

As I read the docs (http://tinyurl.com/3ww9scr), the following two calls
should result in the same object:

parser = argparse.ArgumentParser(description="blah")
parser = argparse.ArgumentParser("blah")

In the first case, I'm explicitly setting description to "blah", in the
second case, I'm passing "blah" as a positional parameter so it should
be taken as first parameter to the function, which happens to be
description. Either way should end up the same.

I don't, however, get the same behavior when run with "-h". The first
gives what I would expect:

------------------------------------------------
usage: arg.py [-h]

blah

optional arguments:
-h, --help show this help message and exit

 

[Peter Otten]

As I read the docs (http://tinyurl.com/3ww9scr), the following two calls
should result in the same object:

parser = argparse.ArgumentParser(description="blah")
parser = argparse.ArgumentParser("blah")

In the first case, I'm explicitly setting description to "blah", in the
second case, I'm passing "blah" as a positional parameter so it should
be taken as first parameter to the function, which happens to be
description. Either way should end up the same.

I don't, however, get the same behavior when run with "-h". The first
gives what I would expect:

------------------------------------------------
usage: arg.py [-h]

blah

optional arguments:
-h, --help show this help message and exit
------------------------------------------------

and the second gives:

------------------------------------------------
usage: blah [-h]

optional arguments:
-h, --help show this help message and exit

A quick look into the source code reveals the the documentation is not
consistent with the actual implementation:

http://hg.python.org/cpython/file/eef1027ab2f0/Lib/argparse.py#l1581

"""
class ArgumentParser(_AttributeHolder, _ActionsContainer):
[...]
def __init__(self,
prog=None,
usage=None,
description=None,
epilog=None,
version=None,
parents=[],
formatter_class=HelpFormatter,
prefix_chars='-',
fromfile_prefix_chars=None,
argument_default=None,
conflict_handler='error',
add_help=True):
"""

I suggest that you file a bug report.

PS: My guess is that you are supposed to use keyword parameters only, but
that the implementation doesn't enforce that (yet?).

 

[Roy Smith]

As I read the docs (http://tinyurl.com/3ww9scr), the following two calls
should result in the same object:

parser = argparse.ArgumentParser(description="blah")
parser = argparse.ArgumentParser("blah")

Sigh. I should have dug deeper before posting. The docs don't match
the code (they list the arguments in different orders).

I've opened http://bugs.python.org/issue13249 on this.

 

[Terry Reedy]

As I read the docs (http://tinyurl.com/3ww9scr), the following two calls
should result in the same object:

parser = argparse.ArgumentParser(description="blah")
parser = argparse.ArgumentParser("blah")

In the first case, I'm explicitly setting description to "blah", in the
second case, I'm passing "blah" as a positional parameter so it should
be taken as first parameter to the function, which happens to be
description. Either way should end up the same.

I don't, however, get the same behavior when run with "-h". The first
gives what I would expect:

------------------------------------------------
usage: arg.py [-h]

blah

optional arguments:
-h, --help show this help message and exit
------------------------------------------------

and the second gives:

------------------------------------------------
usage: blah [-h]

optional arguments:
-h, --help show this help message and exit

A quick look into the source code reveals the the documentation is not
consistent with the actual implementation:

http://hg.python.org/cpython/file/eef1027ab2f0/Lib/argparse.py#l1581

"""
class ArgumentParser(_AttributeHolder, _ActionsContainer):
[...]
def __init__(self,
prog=None,
usage=None,
description=None,
epilog=None,
version=None,
parents=[],
formatter_class=HelpFormatter,
prefix_chars='-',
fromfile_prefix_chars=None,
argument_default=None,
conflict_handler='error',
add_help=True):
"""

I would call this a doc bug. The explanation of the parameters is in a
different order yet. That should be changed too.

help(ArgumentParser) gives them in the actual order.

I suggest that you file a bug report.

PS: My guess is that you are supposed to use keyword parameters only,

Parameters are just names local to the function. They are matched to
argument objects by position or keyword, unless positional matching is
disabled with the '*,' syntax, or unless the function is 'builtin' and
keyword matching is not enabled.

but that the implementation doesn't enforce that (yet?).

This would be an easy change in that adding '*, ' after 'self, ' in the
parameter list would do it. It would be difficult in that it could break
code that uses positional matching correctly, as given in the help
message, and there is no way I know of to give a deprecation message.
But there might be very little code that does so, given the
mis-documentation in the manual.