Queue using Stack.py

'''##Description
Complete the function of push and pop and front for a queue, stack object names are S1 and S2.
Expected Time complexity is O(N) for push and O(1) for pop and front.

#Input Description
This is a function complete problem. You just have to complete the function. The input format given below is just for your understanding.
The first line of the input contains Q, the number of queries to be executed.
Each query X is of type X = 0, X = 1 or X = 2.
Query X = 0 indicates, an element Y to be pushed into the queue.
Query X = 2 indicates, an element to be removed from the queue.
Query X = 1 indicates, an element to be peeked from the queue.

#Output Description
For each query of type X = 1, print the value at the front of the queue.

##Sample Input 1
6
0 1
0 2
0 3
1 
2
1
##Sample Output 1
1
2

##Solution-'''
class Queue:
    def __init__(self):
        self.s1 = []  
        self.s2 = []

    def enqueue(self, value):
        # add element
      self.s1.append(value)

    def dequeue(self):
        # Pop and return top element
      if not self.s2:
        while self.s1:
          self.s2.append(self.s1.pop())
      if not self.s2:
        return None
      return self.s2.pop()
        

    def peek(self):
      if not self.s2:
        while self.s1:
          self.s2.append(self.s1.pop())
      if not self.s2:
        return None
      return self.s2[-1]

    def isEmpty(self):
        return len(self.s1)==0 or len(self.s2)==0