Reputation: 15632
Need a way to check if an object is an instance of any class in some particular module.
I know I can do it by explicitly importing every class from that module and checking with a tuple:
from my_module import ClassOne, ClassTwo
>>> isinstance(my_obj, (ClassOne, ClassTwo))
True
But in reality, the module I'm importing from has a TON of classes in it, and seems needlessly verbose to import them all explicitly, use them to build a huge tuple, and type check against it. I've tried a few things to avoid this:
import my_module
# Test my_obj against the module itself
>>> isinstance(my_obj, my_module)
TypeError: isinstance() arg 2 must be a class, type, or tuple of classes and types
# Try to test against a wildcard attribute on my_module
>>> isinstance(my_obj, my_module.*)
SyntaxError: invalid syntax
#Try to build a tuple of clases with iteration to check against
>>> for klass in my_module:
TypeError: 'module' object is not iterable
Is there a way to type check against ALL the classes in my_module, without explicitly naming them in a tuple?
Optional Background Info:
I may be overlooking a better way to approach my problem -- if you are wondering, here's the situation:
We are exporting data from a Google App Engine app to an app we have hosted on Rackspace. We are serializing the data with pickle
and then sending it over to our Rackspace server with HTTP Requests.
Some of the data in the Google App Engine database is of GAE-specific data-types, imported from google.appengine.api.datastore_types. If any of these data types go across the wire to our Rackspace server, they will raise an error depickling, because our Rackspace app doesn't have the required GAE libraries. So, on the way out of GAE, I'm checking to see if any of the outgoing objects have a type from google.appengine.api.datastore_types. If they do, I either convert them to a builtin data-type or I delete the field off the object.
Upvotes: 36
Views: 25684
Reputation: 1043
The other solutions suggested testing getattr(obj, '__module__', None) == module.__name__
for boolean True
or False
. This only works if the object class is a direct member of the module. It will fail if a submodule is involved.
For instance, suppose you are doing calculations with experimental numerical data, interpolating measured points using scipy.interpolate.interp1d. You store your interpolation function in variable f
. Then
> print(f.__module__)
scipy.interpolate._interpolate
The module is identified as the submodule scipy.interpolate, not simply scipy.
If what you're trying to do is to check if your object class comes from scipy, the suggested test will fail. If f = scipy.interpolate.interp1d
, then the result is
> print(getattr(f, '__module__', None) == scipy.__name__)
False
Instead, you want the pattern
module.__name__ in getattr(obj, '__module__', [])
e.g.
> print(scipy.__name__ in getattr(f, '__module__', []))
True
getattr
should be given a default value []
rather than None
in order for in
to work successfully in the cases where this empty default value is used.
Upvotes: 3
Reputation: 1311
I have used @mgilson simple solution:
from somewhere import module
if getattr(obj, '__module__', None) == module.__name__:
# obj is from module.
and noticed that if you have a tree of modules, and you want to make sure it comes from the base module, you have to do:
from somewhere import module
if getattr(obj, '__module__', None).split('.')[0] == module.__name__:
# obj is from module.
But if your object
is from a built-in it'll rise an exception, so I'd:
from somewhere import module
module_tree = getattr(obj, '__module__', None)
parent = module_tree.split('.')[0] if module_tree else None
if parent == module.__name__:
# obj is from module.
Upvotes: 2
Reputation: 310197
You can use inspect.getmembers
to get all the classes in your module:
inspect.getmembers(my_module,inspect.isclass)
This will return a list of name-class pairs. You just want the classes:
my_module_classes = tuple(x[1] for x in inspect.getmembers(my_module,inspect.isclass))
One thing that I managed to overlook when I initially wrote this answer is the ability to check a class's __module__
attribute. You might be able to get away with checking if the __module__
is what you expect it to be:
from somewhere import module
if getattr(obj, '__module__', None) == module.__name__:
# obj is from module.
This is likely to be cheaper than isinstance
checking against a large list of class names.
Upvotes: 22