命令模式和迭代器模式 13/30 | Python 主题月

写在前面

本文正在参加「Python主题月」，详情查看活动链接

这个月是 Python 活动月，我决定尝试用 Python 来刷这 30 天的每日一题和随机一题。然后如果周末有精力，我想捣鼓捣鼓这个python-patterns

设计模式对我来说更多的是学习而不是我的个人经验总结，所以我很可能理解偏，如果有大佬见到了请及时指出，我之所以选择在掘金来写一些个人的东西是因为这里的文章质量更高，我不希望后来者看到了这些文章被误导。

命令模式

from typing import Union


class HideFileCommand:
    """
    A command to hide a file given its name
    """

    def __init__(self) -> None:
        # an array of files hidden, to undo them as needed
        self._hidden_files = []

    def execute(self, filename: str) -> None:
        print(f"hiding {filename}")
        self._hidden_files.append(filename)

    def undo(self) -> None:
        filename = self._hidden_files.pop()
        print(f"un-hiding {filename}")


class DeleteFileCommand:
    """
    A command to delete a file given its name
    """

    def __init__(self) -> None:
        # an array of deleted files, to undo them as needed
        self._deleted_files = []

    def execute(self, filename: str) -> None:
        print(f"deleting {filename}")
        self._deleted_files.append(filename)

    def undo(self) -> None:
        filename = self._deleted_files.pop()
        print(f"restoring {filename}")


class MenuItem:
    """
    The invoker class. Here it is items in a menu.
    """

    def __init__(self, command: Union[HideFileCommand, DeleteFileCommand]) -> None:
        self._command = command

    def on_do_press(self, filename: str) -> None:
        self._command.execute(filename)

    def on_undo_press(self) -> None:
        self._command.undo()


def main():
    """
    >>> item1 = MenuItem(DeleteFileCommand())
    >>> item2 = MenuItem(HideFileCommand())
    # create a file named `test-file` to work with
    >>> test_file_name = 'test-file'
    # deleting `test-file`
    >>> item1.on_do_press(test_file_name)
    deleting test-file
    # restoring `test-file`
    >>> item1.on_undo_press()
    restoring test-file
    # hiding `test-file`
    >>> item2.on_do_press(test_file_name)
    hiding test-file
    # un-hiding `test-file`
    >>> item2.on_undo_press()
    un-hiding test-file
    """


if __name__ == "__main__":
    import doctest

    doctest.testmod()

迭代器模式

def count_to(count):
    """Counts by word numbers, up to a maximum of five"""
    numbers = ["one", "two", "three", "four", "five"]
    yield from numbers[:count]


# Test the generator
def count_to_two() -> None:
    return count_to(2)


def count_to_five() -> None:
    return count_to(5)


def main():
    """
    # Counting to two...
    >>> for number in count_to_two():
    ...     print(number)
    one
    two
    # Counting to five...
    >>> for number in count_to_five():
    ...     print(number)
    one
    two
    three
    four
    five
    """


if __name__ == "__main__":
    import doctest

    doctest.testmod()

小结

参考文献

• 无