I am a bit lost about how isinstance() works in Python. I have used the function before, and the behavior was quite clear, until now.
A bit of context. I have a class Classifier which has a method set_kernel that can take a string or a Kernel as the parameter. I am creating from the main function an object of the Kernel type called k. When I use isinstance(k, Kernel) the answer is True. However, if I pass k as parameter to the classifier, and then I do the same check inside the function, it returns False.
Any clue about what is going on here? I attach some code snippet to make it clearer:
class Kernel(object):
pass
class Gaussian(Kernel):
pass
class Classifier():
def set_kernel(kernel, *args):
print isinstance(kernel, Kernel) # This prints False
k = Gaussian() # This is a son of Kernel
print isinstance(k, Kernel) # This prints True
c = Classifier()
c.set_kernel(k) # This prints False, check above
Thanks!
Edit 1: I have improved the coded and cleaned all the things that are not related with the problem itself.
If your set_kernel function is not a staticmethod the first argument is the instance if you call this function on an instance. See for example:
class Classifier():
def set_kernel(kernel, *args):
print(kernel)
print(isinstance(kernel, int))
>>> k = 10
>>> print(k)
10
>>> print(isinstance(k, int))
True
>>> c = Classifier()
>>> c.set_kernel(k)
<__main__.Classifier object at 0x0000020FABD0FDA0>
False
If you however make it a staticmethod it "works":
class Classifier():
@staticmethod
def set_kernel(kernel, *args):
print(kernel)
print(isinstance(kernel, int))
>>> k = 10
>>> print(k)
10
>>> print(isinstance(k, int))
True
>>> c = Classifier()
>>> c.set_kernel(k)
10
True
or if you don't want it to be static insert another argument for the instance, typically called "self" in the parameter list:
class Classifier():
def set_kernel(self, kernel, *args):
print(kernel)
print(isinstance(kernel, int))