Simple queue in Python

queue.py

# Author: Michelle Mackie
# Update: Ivan E. Cao-Berg
#
# Copyright (C) 2012-2025
# School of Computer Science
# Carnegie Mellon University
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published
# by the Free Software Foundation; either version 2 of the License,
# or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.
#
# For additional information visit http://www.andrew.cmu.edu/~icaoberg or
# send email to [email protected]

class Queue:
    def __init__(self):
        """
        Initializes an empty queue.
        """
        self.queue = []

    def push(self, value):
        """
        Adds a value to the end of the queue.

        Args:
            value (Any): The value to add to the queue.

        Returns:
            bool: True if the value was successfully added, False otherwise.
        """
        if value is None:
            return False

        self.queue.append(value)
        return True

    def peek(self):
        """
        Returns the front value of the queue without removing it.

        Returns:
            Any: The front value of the queue, or None if the queue is empty.
        """
        return self.queue[0] if self.queue else None

    def pop(self):
        """
        Removes and returns the front value from the queue.

        Returns:
            bool: True if a value was successfully removed, False otherwise.
        """
        if self.queue:
            self.queue.pop(0)
            return True
        return False

    def size(self):
        """
        Returns the number of elements in the queue.

        Returns:
            int: The size of the queue.
        """
        return len(self.queue)

    def contains(self, value):
        """
        Checks if the queue contains a specific value.

        Args:
            value (Any): The value to check for.

        Returns:
            bool: True if the value exists in the queue, False otherwise.
        """
        return value in self.queue

    def clear(self):
        """
        Clears all elements from the queue.
        """
        self.queue.clear()

    def is_empty(self):
        """
        Checks if the queue is empty.

        Returns:
            bool: True if the queue is empty, False otherwise.
        """
        return len(self.queue) == 0