Optimized stack implementation which give minimum element from stack in O(1) time.

stacks.py

class Stack(object):
    """docstring for Stack"""
    def __init__(self):
        self.stack = []
        self.min_stack = []

    def push(self, x):
        if self.isEmpty():
            self.stack.append(x)
            self.min_stack.append(x)
        else:
            self.stack.append(x)
            mini = self.min_stack[-1]

            if x <= mini:
                self.min_stack.append(x)

    def isEmpty(self):
        return self.stack == []
    
    def peek(self):
        if not self.isEmpty():
            return self.stack[-1]
        return 0

    def pop(self):
        if self.isEmpty():
            print "Stack is empty.Can not pop anymore."
        res = self.stack.pop()
        if res == self.min_stack[-1]:
            self.min_stack.pop()

        return res

    def getMin(self):
        return self.min_stack[-1]