Leetcode (Python): Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.
For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3. 

Solution:

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    # @param head, a ListNode
    # @return a ListNode
    def deleteDuplicates(self, head):
        pointer = head;
        while pointer != None and pointer.next !=None:
            if pointer.val == pointer.next.val:
                pointer.next = pointer.next.next
            else:
                pointer = pointer.next
        return head