New submission from Barry A. Warsaw:
Run the following code snippet:
-----snip snip-----
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("--test", dest="test", type=str,
default=[], action='append')
args = parser.parse_args()
print args.test, repr(args.test)
-----snip snip-----
In Python 3.3 (with the appropriate syntactic changes), args.test is clearly a
list. In Python 2.7 and 3.2, args.test is the string "[]". I can't tell from
reading the docs what the expected value should be, but intuitively, the Python
3.3 behavior makes the most sense, i.e. that args.test is a list, not the
string representation of a list!
Removing type=str from add_argument() "fixes" the value, but that doesn't seem
right because str is the default type so that should have no effect.
We discovered this when we tried to do args.test.append('foo') and tracebacked
because args.test wasn't a list.
Original bug report in Ubuntu: https://launchpad.net/bugs/1048710
but I've tested this with upstream hg head for 2.7, 3.2, and 3.3. It works in
Ubuntu's 3.3rc2 but not in upstream head 3.3rc2+, so from reading Misc/NEWS I
think the fix for issue #12776 and issue #11839 might be involved.
----------
messages: 170202
nosy: barry
priority: normal
severity: normal
status: open
title: argparse add_argument() confusing behavior when type=str, default=[],
action='append'
versions: Python 2.7, Python 3.2
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue15906>
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