[issue41534] argparse : allow_abbrev behavior between 3.7 and 3.8

[Steve Fox]

Steve Fox  added the comment:

Fundamentally the use of allow_abbrev=False is now broken (it is allowing 
abbreviations when already explicitly told not to)

The use of a single - for all options is much older than -- and exists in my 
unix utilities and many programs have been written to follow this convention, 
these are now broken in 3.8+

"Changed in version 3.8: In previous versions, allow_abbrev also disabled 
grouping of short flags such as -vv to mean -v -v"

Does not accurately describe the behavior change, it is more broadly injecting 
abbreviations when already told not to.

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nosy: +Fox214

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[issue41534] argparse : allow_abbrev behavior between 3.7 and 3.8

[paul j3]

paul j3  added the comment:

I'm going to close this.  3.8 works as expected/documented, provided we use the 
normal  double dash protocol for long options.  Single dash is best reserved 
for single character options, where chaining is allowed.

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stage:  -> resolved
status: open -> closed

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[issue41534] argparse : allow_abbrev behavior between 3.7 and 3.8

[paul j3]

paul j3  added the comment:

In your first example:

In [29]: parser = argparse39.ArgumentParser(allow_abbrev=True)  
In [30]: parser.add_argument('-o'); 

In [32]: parser.parse_known_args(['-o','test']) 
Out[32]: (Namespace(o='test'), [])

In [33]: parser.parse_known_args(['-object','test'])
Out[33]: (Namespace(o='bject'), ['test'])

Here the '-object' is interpreted as '-o' flag, with value the rest of the 
string.  That's normal behavior for a short option.

In [34]: parser.parse_known_args(['-o','test1','-object','test2'])  
Out[34]: (Namespace(o='bject'), ['test2'])

Same thing only '-object' has overwritten the 'test1' value.

In your second example:

In [39]: parser = argparse39.ArgumentParser(allow_abbrev=False) 
In [40]: parser.add_argument('-verbose');   

In [42]: parser.parse_known_args(['-v', '-verbose=2'])  
usage: ipython3 [-h] [-verbose VERBOSE]
ipython3: error: argument -verbose: expected one argument

Expected uses:

In [46]: parser.parse_known_args(['-verbose','two'])
Out[46]: (Namespace(verbose='two'), [])
In [47]: parser.parse_known_args(['-verbose=2'])
Out[47]: (Namespace(verbose='2'), [])

The '-ver' is not accepted as abbreviation:

In [48]: parser.parse_known_args(['-ver=2'])
Out[48]: (Namespace(verbose=None), ['-ver=2'])

'allow_abbrev' doesn't have effect because of '-verbose'

If instead I define '--verbose', I can turn the abbrev on/off:

In [49]: parser = argparse39.ArgumentParser(allow_abbrev=False) 
In [50]: parser.add_argument('--verbose');  
In [51]: parser.parse_known_args(['-ver=2'])
Out[51]: (Namespace(verbose=None), ['-ver=2'])
In [52]: parser.parse_known_args(['--ver=2'])   
Out[52]: (Namespace(verbose=None), ['--ver=2'])
In [53]: parser.allow_abbrev=True   
In [54]: parser.parse_known_args(['--ver=2'])   
Out[54]: (Namespace(verbose='2'), [])

There are a lot of variations to examine here.  The original, the 3.7, and 3.8 
versions.  abbrev False or True.  Proper long option (--), improper etc.

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[issue41534] argparse : allow_abbrev behavior between 3.7 and 3.8

[r1kk3r]

r1kk3r  added the comment:

Another issue:

parser = argparse.ArgumentParser(allow_abbrev=False)
parser.add_argument('-verbose', type=int, required=True, dest="bla", help="bla")
known_args, rest_of_args = parser.parse_known_args(["-v", "-verbose=2"])

With python 3.8.5

test.py: error: argument -verbose: expected one argument

With python 3.7.8




This is really annoying. Argparse tries to do "smart" things where it 
shouldn't. I want it to parse -verbose, I never told him that -v is an alias 
for -verbose...

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[issue41534] argparse : allow_abbrev behavior between 3.7 and 3.8

[Ned Deily]

Change by Ned Deily :


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nosy: +petr.viktorin

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[issue41534] argparse : allow_abbrev behavior between 3.7 and 3.8

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

Bisection tells me this was introduced with commit 
b1e4d1b6032d4c82b549233fa08a2c7cfe7e818b in issue26967

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nosy: +xtreak

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[issue41534] argparse : allow_abbrev behavior between 3.7 and 3.8

[hai shi]

Change by hai shi :


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nosy: +paul.j3, rhettinger

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[issue41534] argparse : allow_abbrev behavior between 3.7 and 3.8

[r1kk3r]

New submission from r1kk3r :

I looked into changelog and the source code to see if the behavior was wanted 
but I was not able to see the source of the issue.

import argparse
parser = argparse.ArgumentParser(allow_abbrev=True)
parser.add_argument('-o', type=str, required=True, dest="bla", help="bla")
known_args, rest_of_args = parser.parse_known_args(["-o", "test1", 
"-object_lto", "test2"])
print(rest_of_args)

Executing with python 3.7.8

With allow_abbrev=True:

['test2']

allow_abbrev=False:

['-object_lto', 'test2']


Executed with python 3.8.5

With allow_abbrev=True:

['test2']

allow_abbrev=False:

['test2']


Is it expected? How do I get the behavior of python 3.7 in python 3.8?

--
components: Library (Lib)
messages: 375276
nosy: r1kk3r
priority: normal
severity: normal
status: open
title: argparse : allow_abbrev behavior between 3.7 and 3.8
type: behavior
versions: Python 3.8

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