desbma added the comment:
I came up with something that satisfies my needs (no boilerplate code, and
intuitive add_argument call).
I modified your factory, and defined a simple action class (this is a quick and
dirty prototype for discussion, I am in no way asking that such thing should be
merged as such):
class EnumType(object):
"""Factory for creating enum object types
"""
def __init__(self, enumclass, action):
self.enums = enumclass
self.action = action
def __call__(self, astring):
name = self.enums.__name__
try:
v = self.enums[astring.upper()]
except KeyError:
msg = ', '.join([t.name.lower() for t in self.enums])
msg = '%s: use one of {%s}'%(name, msg)
raise argparse.ArgumentTypeError(msg)
else:
self.action.choices = None # hugly hack to prevent post validation
from choices
return v
def __repr__(self):
astr = ', '.join([t.name.lower() for t in self.enums])
return '%s(%s)' % (self.enums.__name__, astr)
class StoreEnumAction(argparse._StoreAction):
def __init__(self,
option_strings,
dest,
type,
nargs=None,
const=None,
default=None,
required=False,
help=None,
metavar=None):
super().__init__(option_strings=option_strings,
dest=dest,
nargs=nargs,
const=const,
default=default,
type=EnumType(type, self),
choices=tuple(t.name.lower() for t in type),
required=required,
help=help,
metavar=metavar)
Then all I have to do is to pass 'action=StoreEnumAction, type=TheEnum' to the
add_argument call.
The good:
I get a proper usage line (which takes into account the value of 'nargs'),
relevant error messages, and what is stored in the namespace after validation
is the proper enum type, not a string.
The bad:
* The reference to the action inside the factory is ugly. This should probably
be refractored to be all contained inside StoreEnumAction.
* The meaning of the 'type' parameter for StoreEnumAction is somewhat different
than for other actions (enum class vs callable that validates)
What do you think?
----------
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue25061>
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