[PyGame] TypeError: unsupported operand type(s) for -: 'int' and 'instancemethod'

[nilamo]

A function defined in the class is already bound to the instance.  You call it just as you would any function, with parentheses.

>>> class Spam:
...   def __init__(self, foo):
...     self.bar = foo
...   def quz(self):
...     print("I'm an instance method!")
...     return self.bar
...
>>> thing = Spam(42)
>>> thing.quz()
I'm an instance method!
42