Author: OhiyoX

"""
思路：
1、建立next_list,next_list[i]表示当pattern[i]不匹配时，跳转的pattern最大公共区域的下一级值。
"""

s = 'abdabdabababaaababac'
p = 'ababaaababac'
lens, lenp = len(s), len(p)


def build_next():
    next_list = [0] * lenp
    for i in range(1, lenp):
        if p[i] == p[next_list[i - 1]]:
            next_list[i] = next_list[i - 1] + 1
    return next_list


def kmp_match():
    i = 0
    j = 0
    next_list = build_next()
    while i < len(s):
        if lens - i >= lenp - j:
            if s[i] == p[j]:
                i += 1
                j += 1
            elif j == 0:
                i += 1
            else:
                j = next_list[j - 1]
        else:
            return -1
    return lens - j


print('next_list: ', build_next())
print('match_at: ', kmp_match())

def async_down_image(urls_dict, save_dirpath):
    async def down_image(client, url, save_path):
        root, name = os.path.split(save_path)
        if os.path.exists(save_path):
            return True
        try_count = 0
        while try_count < 3:
            try:
                async with client.get(url) as resp:
                    if resp.status == 200:
                        content = await resp.read()
                        print(f"Downloading {name}")
                        with open(save_path, 'wb') as fp:
                            fp.write(content)
                        return True
                    else:
                        try_count += 1
                        await asyncio.sleep(try_count)
            except:
                try_count += 1
                await asyncio.sleep(try_count)
        return False

    async def main(urls):
        async with aiohttp.ClientSession() as client:
            tasks = []
            for filename, url in urls.items():
                save_path = os.path.join(save_dirpath, filename)
                tasks.append(
                    asyncio.create_task(down_image(client, url, save_path=save_path))
                )
            await asyncio.wait(tasks)

    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
    asyncio.run(main(urls_dict))

花了好多天去理解unittest.main()和Base.metadata.create_all()的实现方式，如何在不实例化的情况下知道子类的信息？

以下为实验代码，详细参考《Python Cookbook（第3版）中文版》

class Metaclass(type):
    childs = []
    def __init__(self, clsname, bases, clsdict):
        super().__init__(clsname, bases, clsdict)
        self.childs.append(clsname)

class Base(metaclass=Metaclass):
    pass


class Tree1(Base):
    pass

class Tree2(Base):
    pass

if __name__ == '__main__':
    for c in Base.childs:
        print(c)

输出结果：

Base
Tree1
Tree2

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