Determine if Python variable is an instance of a built-in type

This is an old question but it seems none of the answers actually answer the specific question: "(How-to) Determine if Python variable is an instance of a built-in type". Note that it's not "[...] of a specific/given built-in type" but of a.

The proper way to determine if a given object is an instance of a buil-in type/class is to check if the type of the object happens to be defined in the module __builtin__.

def is_builtin_class_instance(obj):    return obj.__class__.__module__ == '__builtin__'

Warning: if obj is a class and not an instance, no matter if that class is built-in or not, True will be returned since a class is also an object, an instance of type (i.e. AnyClass.__class__ is type).

The best way to achieve this is to collect the types in a list of tuple called primitiveTypes and:

if isinstance(myvar, primitiveTypes): ...

The types module contains collections of all important types which can help to build the list/tuple.

Works since Python 2.2

Not that I know why you would want to do it, as there isn't any "simple" types in Python, it's all objects. But this works:

type(theobject).__name__ in dir(__builtins__)

But explicitly listing the types is probably better as it's clearer. Or even better: Changing the application so you don't need to know the difference.

Update: The problem that needs solving is how to make a serializer for objects, even those built-in. The best way to do this is not to make a big phat serializer that treats builtins differently, but to look up serializers based on type.

Something like this:

def IntSerializer(theint):    return str(theint)def StringSerializer(thestring):    return repr(thestring)def MyOwnSerializer(value):    return "whatever"serializers = {    int: IntSerializer,    str: StringSerializer,    mymodel.myclass: MyOwnSerializer,}def serialize(ob):    try:        return ob.serialize() #For objects that know they need to be serialized    except AttributeError:        # Look up the serializer amongst the serializer based on type.        # Default to using "repr" (works for most builtins).        return serializers.get(type(ob), repr)(ob)

This way you can easily add new serializers, and the code is easy to maintain and clear, as each type has its own serializer. Notice how the fact that some types are builtin became completely irrelevant. :)