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Implement Iterator Pattern

Table of contents

What is Iterator pattern for?
Implement Of Iterator Pattern

What is Iterator pattern for?

This pattern use for iterate condition and decouple algorithms from containers. for example you want iterate in two or more way:

iterate list
iterate array

Implement Of Iterator Pattern

interface.py implement like below

Python

import abc
class IteratorInterface(metaclass=abc.ABCMeta):
    @classmethod
    def __subclasshook__(cls, subclass):
        return (
            hasattr(subclass, 'hasnext') and
            callable(subclass.hasnext) and
            hasattr(subclass, 'current') and
            callable(subclass.current) and
            hasattr(subclass, 'next') and
            callable(subclass.next) or
            NotImplemented
        )
    @abc.abstractmethod
    def hasnext(self) -> bool:
        raise NotImplementedError
    @abc.abstractmethod
    def current(self):
        raise NotImplementedError
    @abc.abstractmethod
    def next(self):
        raise NotImplementedError

This is a formal approch of interface in pyhton.

browser_history.py implement like below

Python

from iterator_interface import IteratorInterface
from typing import List
class BrowserHistory:
    def __init__(self):
        self.urls = []
    def push(self, url: str):
        self.urls.append(url)
    def pop(self) -> str:
        return self.urls.pop()
    def createIterator(self) -> IteratorInterface:
        return self.ArrayIterator(self)
    class ArrayIterator(IteratorInterface):
        def __init__(self, history):
            self.index = 0
            self.history = history
        def hasnext(self) -> bool:
            return (self.index < len(self.history.urls))
        def current(self) -> str:
            return self.history.urls[self.index]
        def next(self):
            self.index += 1

In this file we implement ArrayIterator for iterat in the array if in futuer we decide to change the data structuer we can implement new class.

main.py implement like below

Python

from browser_history import BrowserHistory
def main():
    print('start')
    browser = BrowserHistory()
    browser.push('pornhub.com')
    browser.push('google.com')
    browser.push('yahoo.com')
    browser.push('varzesh3.com')
    print('push complete')
    iterator = browser.createIterator()
    while(iterator.hasnext()):
        print(iterator.current())
        iterator.next()
if __name__ == '__main__':
    main()

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