New submission from Chris Jerdonek: In argparse, positional arguments with nargs='*' default to [] rather None, even if default=None is passed explicitly. The documentation says otherwise:
"The default keyword argument of add_argument(), whose value defaults to None, specifies what value should be used if the command-line argument is not present. ... For positional arguments with nargs equal to ? or *, the default value is used when no command-line argument was present:" (from http://docs.python.org/dev/library/argparse.html#default ) import argparse def parse(args, **kwargs): parser = argparse.ArgumentParser() parser.add_argument('foo', **kwargs) ns = parser.parse_args(args) print(repr(ns.foo)) parse([], nargs='?') # None parse([], nargs='*') # [] <-- parse([], nargs='*', default=None) # [] <-- parse([], nargs='*', default=False) # False parse([], nargs='*', default=0) # 0 Three options include (there may be more): (1) document the behavior (2) make a default of None yield None (3) do (2), but change the default to [] instead of None when nargs='*' ---------- components: Library (Lib) messages: 179174 nosy: bethard, chris.jerdonek priority: normal severity: normal status: open title: argparse: positional args with nargs='*' defaults to [] type: behavior versions: Python 2.7, Python 3.2, Python 3.3, Python 3.4 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue16878> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
