A queue implementation using only two stacks and whose methods only use standard stack operations (push, pop, peek, size)

StackQueue.py

import functools 

class StackQueue:
    def __init__(self):
        self.main = []
        self.aux = []
    
    def __repr__(self):
        return f'StackQueue(self.main={self.main}, self.aux={self.aux})'
    
    def prepare_dequeue(method):
        @functools.wraps(method)
        def wrapper(self, *args, **kwargs):
            if not self.aux:
                while self.main:
                    self.aux.append(self.main.pop())
            return method(self, *args, **kwargs)
        return wrapper
    
    def enqueue(self, x):
        self.main.append(x)
    
    @prepare_dequeue
    def dequeue(self):
        try:
            return self.aux.pop()
        except IndexError as exc:
            raise Exception('Cannot dequeue from empty queue') from exc
    
    @prepare_dequeue
    def peek(self):
        try:
            return self.aux[-1]
        except IndexError as exc:
            raise Exception('Cannot peek at empty queue') from exc
    
    def is_empty(self):
        return not self.main and not self.aux
    
    del prepare_dequeue