Python3.x 如何正确创建自定义文本编解码器

你要的是最低限度的！

• 编写一个编码函数和一个解码函数.
• 编写一个"搜索函数"，返回由上述编码器和解码器构造的CodecInfo个对象.
• 使用codec.register注册一个返回上述CodecInfo对象的函数.

下面是一个按顺序将小写字母a-z转换为0-25的示例.

import codecs
import string

from typing import Tuple

# prepare map from numbers to letters
_encode_table = {str(number): bytes(letter, 'ascii') for number, letter in enumerate(string.ascii_lowercase)}

# prepare inverse map
_decode_table = {ord(v): k for k, v in _encode_table.items()}


def custom_encode(text: str) -> Tuple[bytes, int]:
    # example encoder that converts ints to letters
    # see https://docs.python.org/3/library/codecs.html#codecs.Codec.encode
    return b''.join(_encode_table[x] for x in text), len(text)


def custom_decode(binary: bytes) -> Tuple[str, int]:
    # example decoder that converts letters to ints
    # see https://docs.python.org/3/library/codecs.html#codecs.Codec.decode
    return ''.join(_decode_table[x] for x in binary), len(binary)


def custom_search_function(encoding_name):
    return codecs.CodecInfo(custom_encode, custom_decode, name='Reasons')


def main():

    # register your custom codec
    # note that CodecInfo.name is used later
    codecs.register(custom_search_function)

    binary = b'abcdefg'
    # decode letters to numbers
    text = codecs.decode(binary, encoding='Reasons')
    print(text)
    # encode numbers to letters
    binary2 = codecs.encode(text, encoding='Reasons')
    print(binary2)
    # encode(decode(...)) should be an identity function
    assert binary == binary2

if __name__ == '__main__':
    main()

运行这个 fingerprint

$ python codec_example.py
0123456
b'abcdefg'

有关Codec界面的详细信息，请参见https://docs.python.org/3/library/codecs.html#codec-objects.尤其是解码功能

... 解码对象input并返回元组(输出对象，长度

而编码功能

... 对对象input进行编码并返回一个元组(输出对象，消耗的长度).

请注意，您还应该担心处理流、增量编码/解码以及错误处理.有关更完整的示例，请参阅@krs013提到的hexlify codec.

另外，你也可以用codec.open(..., encoding='Reasons')代替codec.decode.