[issue11839] argparse: unexpected behavior of default for FileType('w')

[Roundup Robot]

Roundup Robot added the comment:

New changeset 1b614921aefa by R David Murray in branch '3.2':
#12776,#11839: call argparse type function only once.
http://hg.python.org/cpython/rev/1b614921aefa

New changeset 74f6d87cd471 by R David Murray in branch 'default':
Merge #12776,#11839: call argparse type function only once.
http://hg.python.org/cpython/rev/74f6d87cd471

New changeset 62b5667ef2f4 by R David Murray in branch '2.7':
#12776,#11839: call argparse type function only once.
http://hg.python.org/cpython/rev/62b5667ef2f4

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[issue11839] argparse: unexpected behavior of default for FileType('w')

[Paolo Elvati]

Changes by Paolo Elvati :


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status: open -> closed

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[issue11839] argparse: unexpected behavior of default for FileType('w')

[Paolo Elvati]

Changes by Paolo Elvati :


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status: closed -> open

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[issue11839] argparse: unexpected behavior of default for FileType('w')

[Paolo Elvati]

Changes by Paolo Elvati :


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resolution:  -> duplicate
status: open -> closed

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[issue11839] argparse: unexpected behavior of default for FileType('w')

[Mike Meyer]

Mike Meyer  added the comment:

Steven - 12776 indeed fixes this issue. I applied the patch from it to a build 
of todays checkout, verified that my simple test script worked, then wrote some 
test cases for test_argparse.

I've uploaded the patch for that test to both issues. I can't close this as a 
duplicate, though.

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Added file: http://bugs.python.org/file25439/fopatch

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[issue11839] argparse: unexpected behavior of default for FileType('w')

[Steven Bethard]

Steven Bethard  added the comment:

I think Issue 12776, which delays type conversions on defaults, should solve 
this problem, right? If you agree, could you add your code here as a test case 
to that issue and mark this as duplicate?

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[issue11839] argparse: unexpected behavior of default for FileType('w')

[Stefan Pfeiffer]

Stefan Pfeiffer  added the comment:

Happens in 3.2, too...

Would be nice to see that fixed.

Stefan

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[issue11839] argparse: unexpected behavior of default for FileType('w')

[Manveru]

Manveru  added the comment:

I have the same issue with default here with 2.7.

Fortunately I have my own type function so I can prevent is by changing my 
internal state. This is however only a workaround for real bug in the argparse.

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versions: +Python 2.7

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[issue11839] argparse: unexpected behavior of default for FileType('w')

[Paolo Elvati]

New submission from Paolo Elvati :

Hi,
when a default is specified for a file argument that is open with writing 
permission (FileType('w')), the default file is always created even if the 
argument is specified in the command line. 
For example he code:

import argparse 
parser = argparse.ArgumentParser() 
parser.add_argument( 
"-o", 
default = 'fake', 
dest = 'OutputFile', 
type = argparse.FileType('w') 
) 
args = parser.parse_args() 

will create the empty file "fake" even if the -o option is given. 
The value inside the code of args.Outputfile is not affected.

Paolo

--
components: Library (Lib)
messages: 133598
nosy: Paolo.Elvati, bethard
priority: normal
severity: normal
status: open
title: argparse: unexpected behavior of default for FileType('w')
type: behavior
versions: Python 3.2

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