[Bug 1048710] Re: Regression in argparse for Python 2.7, 3.2 and 3.3

Launchpad Bug Tracker 1048710 at bugs.launchpad.net
Sat Sep 15 10:25:12 UTC 2012

This bug was fixed in the package python3.2 - 3.2.3-6ubuntu2

python3.2 (3.2.3-6ubuntu2) quantal; urgency=low

  * Update to 20120915 from the 3.2 branch. Linux relevant fixes:
    - Issue #15842: the SocketIO.{readable,writable,seekable} methods now
      raise ValueError when the file-like object is closed.
    - Issue #15906: Fix a regression in argparse caused by the preceding change,
      when action='append', type='str' and default=[]. LP: #1048710.
    - Issue #15793: Stack corruption in ssl.RAND_egd().
 -- Matthias Klose <doko at ubuntu.com>   Sat, 15 Sep 2012 12:14:18 +0200

** Changed in: python3.2 (Ubuntu)
       Status: Confirmed => Fix Released

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  Regression in argparse for Python 2.7, 3.2 and 3.3

Status in Python:
  Fix Released
Status in “python2.7” package in Ubuntu:
  Fix Released
Status in “python3.2” package in Ubuntu:
  Fix Released

Bug description:
  Using the following example:

  import argparse

  parser = argparse.ArgumentParser()
  parser.add_argument("--test", dest="test", type=str,
      default=[], action='append')

  args = parser.parse_args()


  Then running it with simply "python test.py" (WITHOUT passing --test), you get the following:
  Traceback (most recent call last):
    File "test.py", line 11, in <module>
  AttributeError: 'str' object has no attribute 'append'

  My understanding of argparse is that when using both default=[] and
  action="append", args.test should always be a list, empty if not
  passing --test or a list containing the --test values if passed. After
  the recent update, it seems to instead default to an empty string.

  This must somehow be related to the type field as for some reason,
  removing "type=str" fixes the issue though I don't really see why and
  it's still a clear regression.

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