In the Python 3.7.0 interpreter, the following evaluates to False. In 3.6.4, it was True:

    c,d = 500,500
    c is d

This seems to be because, in some cases, Python 3.7 fails to intern integers inside tuples:

    a = (500,500)
    print(a[0] is a[1]) # False
    
    a = (500,500,42)
    print(a[0] is a[1]) # False
    
    a = (500,500,'42')
    print(a[0] is a[1]) # False
    
    answer = 42
    a = (500,500,answer)
    print(a[0] is a[1]) # True
    
    a = (500,500,[42])
    print(a[0] is a[1]) # True

    a = [500,500]
    print(a[0] is a[1]) # True

I believe the above should all return True.