Checking if an object is in a determined class python

I'm trying to create a class representing vectors (called Vector) and one representing matrices (called Matrix). The problem arised in defining the matrix-vector product: I don't see errors in the actual implementation, but I tried to add a check before the code to raise an error if the second element wasn't a Vector and it doesn't work.

I tried using the isinstance() function to check if the vector i was interested in was actually a Vector, but it raises a name error.

I'm not able to find any advice about it and I'm certain that it's because I didnt understand how the function works.

Here's my code:

class Vector: #defined in the module Vector
 def __init__(self):
  pass

class Matrix:
 from Vector import Vector  #the module is called Vector as the class
 def __init__(self):
  pass
 def __mul__(self,other): #method called by self*other, if other is vector should perform matrix-vector multiplication
  if isinstance(other,Vector): 
   pass #I didn't write the actual content because the error arises on the condition
  pass


from Matrix import Matrix #the classes were defined in a different module
from Vector import Vector #the classes were defined in a different module

v=Vector()
A=Matrix()
A*v

The error message was:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "Desktop\python\Matrix.py", line 82, in __mul__
    if isinstance(other,Vector):
NameError: global name 'Vector' is not defined

I imported both the classes Vector and Matrix before using the method __mul__ and in the code for the class Matrix I imported the class Vector again so I could use the class Matrix separately.

The classes are defined in two different files saved in the same directory.

Any hint on how to fix the problem?