new-style class instance check

[Richard Gruet]

Hi all,

How to determine that an object o is for sure an instance of a new-style
class, without knowing of which specific class ?
That is, if I define a function:

def isNewStyleClassInstance(o):
pass ## to be completed

... I want to pass the following test:

def C: pass
def CNew(object): pass

assert not isNewStyleClassInstance(C()) # InstanceType
assert isNewStyleClassInstance(CNew())
assert not isNewStyleClassInstance(1) # instance of type int
# and naturally for all other types of o the function should return False.

Richard

 

[Aahz]

How to determine that an object o is for sure an instance of a new-style
class, without knowing of which specific class ?
That is, if I define a function:

def isNewStyleClassInstance(o):
pass ## to be completed

.. I want to pass the following test:

def C: pass
def CNew(object): pass

assert not isNewStyleClassInstance(C()) # InstanceType
assert isNewStyleClassInstance(CNew())
assert not isNewStyleClassInstance(1) # instance of type int
# and naturally for all other types of o the function should return False.

class UserClass(object): pass

class CNew(UserClass): pass

You can automate this within a module by setting __metaclass__.

 

[John Roth]

Hi all,

How to determine that an object o is for sure an instance of a new-style
class, without knowing of which specific class ?
That is, if I define a function:

def isNewStyleClassInstance(o):
pass ## to be completed

.. I want to pass the following test:

def C: pass
def CNew(object): pass

assert not isNewStyleClassInstance(C()) # InstanceType
assert isNewStyleClassInstance(CNew())
assert not isNewStyleClassInstance(1) # instance of type int
# and naturally for all other types of o the function should return False.

The following untested code should work:

import types

def isNewStyleClass(obj):
if type(obj) is types.InstanceType:
if hasattr(obj.__class__, "__mro__"):
return True
return False



John Roth