What does abstract mean in this context?
abstract, python
Solution
This is a trick described here. There's not keyword `abstract` in Python, so, if you won't override this method in some subclass, it'll cause `NotImplementedError`.
Problem
I need some help in understanding a python concept. ``` class TilePuzzleProblem(search.Problem): """ This class is the class for the NxN - blanks tile puzzle problem """ def __init__(self, N, blanks, initial, goal): """ Initialize """ search.Problem.__init__(self, initial, goal) self.N = N self.blanks = blanks def successor(self, state): """ Generate the successors of the given state. Returns a list of (move, successor) pairs""" abstract def h(self, node): abstract ``` Currently the code hangs at the `abstract` part of the function `h(...)`, but I have no idea what `abstract` means, hence can not understand what the problem is.