Containers are objects that implement a __contains__ method (that usually returns a Boolean value). This method is called in the presence of the in keyword of Python.
Something like the following:
element in container
When used in Python becomes this:
container.__contains__(element)
You can imagine how much more readable (and Pythonic!) the code can be when this method is properly implemented.
Let's say we have to mark some points on a map of a game that has two-dimensional coordinates. We might expect to find a function like the following:
def mark_coordinate(grid, coord):
if 0 <= coord.x < grid.width and 0 <= coord.y < grid.height:
grid[coord] = MARKED
Now, the part that checks the condition of the first if statement seems convoluted; it doesn't reveal the intention of the code, it's not expressive, and worst of all it calls...
