why does python inspect.isclass think an instance is a class?
Given the following module:
class Dummy(dict):
def __init__(self, data):
for key, value in data.iteritems():
self.__setattr__(key, value)
def __getattr__(self, attr):
return self.get(attr, None)
__setattr__=dict.__setitem__
__delattr__=dict.__delitem__
foo=Dummy({"one":1, "two":2})
why does foo
show up in the output of inspect.getmembers(..., predicate=inspect.isclass)
?
$ python2.5
Python 2.5.2 (r252:60911, Aug 28 2开发者_如何学JAVA008, 13:13:37)
[GCC 4.1.2 20071124 (Red Hat 4.1.2-42)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import junk
>>> import inspect
>>> inspect.getmembers(junk, predicate=inspect.isclass)
[('Dummy', <class 'junk.Dummy'>), ('foo', {'two': 2, 'one': 1})]
>>> inspect.isclass(junk.foo)
True
I expected that inspect
would only return Dummy
since that is the only class definition in the module. Apparently, though, junk.foo is a class in the eyes of the inspect module. Why is that?
Prior to Python v2.7, inspect.isclass
naively assumed anything with a __bases__
attribute must be a class.
Dummy
's __getattr__
makes Dummy
instances appear to have every attribute (with a value of None
).
Therefore, to inspect.isclass
, foo
appears to be a class.
Note: __getattr__
should raiseAttributeError
when asked for an attribute it does not know about. (This is very different than returning None
.)
First if all great answer Jon-Eric i just wanted to add some stuff:
if you do in ipython (what a great tool):
%psource inspect.isclass
you will get:
return isinstance(object, types.ClassType) or hasattr(object, '__bases__')
which what Jon-Eric said.
but i guess that you use python < 2.6 and this bug was already fixed, this is the code of inspect.isclass() in python2.7:
return isinstance(object, (type, types.ClassType))
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