how to remove a object in a python list

Question

I create a class named point as following:

class point:
    def __init__(self):
        self.x = 0
        self.y = 0

and create a list of point instances:

p1 = point()
p1.x = 1
p1.y = 1
p2 = point()
p2.x = 2
p2.y = 2
p_list = []
p_list.append(p1)
p_list.append(p2)

Now I'd like remove from the list the instance which x = 1 and y = 1, how can I do this?

I try to add a __cmp__ method for class point as following:

class point:
    def __init__(self):
        self.x = 0
        self.y = 0    
    def __cmp__(self, p):
        return self.x==p.x and self.y==p.y

But the following code does not work

r = point()
r.x = 1
r.y = 1
if r in p_list:
    print('correct')
else:
    print('wrong') # it will go here
p_list.remove(r) # it reports 'ValueError: list.remove(x): x not in list'

Answer 1

Your __cmp__ function is not correct. __cmp__ should return -1/0/+1 depending on whether the second element is smaller/equal/greater than self. So when your __cmp__ is called, it returns True if the elements are equal, which is then interpreted as 1, and thus "greater than". And if the elements are non-equal, it returns False, i.e. 0, which is interpreted as "equal").

For two-dimensional points, "greater than" and "smaller than" are not very clearly defined, anyway, so you can just replace your __cmp__ with __eq__ using the same implementation. Your point class should be:

class point:
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y    

    def __eq__(self, p):
        return self.x==p.x and self.y==p.y