不使用 if 语句覆盖函数

Question

三个模型具有ImageField指一种功能，具有if. 是否有任何建议如何在没有 if 的情况下执行此功能？def upload_location(instance, filename):    _, extension = os.path.splitext(filename)    if isinstance(instance, (Story,)):        return f'stories/{instance.id}/cover{extension}'    elif isinstance(instance, (Episode,)):        return f'stories/{instance.story.id}/{instance.index}/cover{extension}'    elif isinstance(instance, (EpisodeSlide,)):        return f'stories/{instance.episode.story.id}/{instance.episode.index}/{instance.id}{extension}

Answer 1

我同意@Dennis：if 语句使代码非常易读。以下是我在不使用if. 也许有更好的方法，例如使用format语句而不是“f-strings”，并且正如@Dennis 建议的那样，也许使用类型作为键。

def upload_location(instance, filename):

    lookup = dict([

        (Story.__name__, lambda instance: f'stories/{instance.id}/cover{extension}'),

        (Episode.__name__, lambda instance: f'stories/{instance.story.id}/{instance.index}/cover{extension}'),

        (EpisodeSlide.__name__, lambda instance: f'stories/{instance.episode.story.id}/{instance.episode.index}/{instance.id}{extension}')

    ])

    _, extension = os.path.splitext(filename)

    loc = lookup[instance.__class__.__name__](instance)

    return loc

print(upload_location(e, "hello.txt"))

print(upload_location(es, "hello.txt"))

print(upload_location(s, "hello.txt"))

stories/1/10/cover.txt

stories/1/10/100.txt

stories/1/cover.txt

再说一遍，if 语句比上面的函数要好得多！！