为什么 base64.b64encode() 返回一个字节对象? [英] Why does base64.b64encode() return a bytes object?

问题描述

base64.b64encode() 的目的是将二进制数据转换为 ASCII 安全的文本".但是，该方法返回一个字节类型的对象:

<预><代码>>>>导入 base64>>>base64.b64encode(b'abc')b'YWJj'

简单地获取输出和 decode() 很容易，但我的问题是:base64.b64encode() 返回 bytes 的意义是什么 而不是 str?

解决方案

base64.b64encode() 函数的目的是将二进制数据转换为 ASCII 安全的文本"

Python 不同意这一点 - base64 被故意归类为 二进制转换.

强制字节和文本分离并禁止隐式转换是 Python 3 中的一个设计决定.Python 现在对此非常严格，以至于 bytes.encode 甚至不存在，因此 b'abc'.encode('base64') 会引发 属性错误.

该语言的观点是字节串对象已经编码.将字节编码为文本的编解码器不适合这种范式，因为当您想从字节域转到文本域时，它是一个解码.请注意，rot13 编码也已从 标准编码 出于同样的原因 - 它不适合 Python 3 范式.

还可以提出一个性能参数:假设 Python 自动处理了 base64 输出的解码，这是一个 ASCII 编码的二进制表示，由来自 binascii 模块，转换为文本域中的 Python 对象.如果你真的想要字节，你只需要通过再次编码为 ASCII 来撤消解码.这将是一个浪费的往返，一个不必要的双重否定.最好选择加入"解码到文本步骤.

The purpose of base64.b64encode() is to convert binary data into ASCII-safe "text". However, the method returns an object of type bytes:

>>> import base64
>>> base64.b64encode(b'abc')
b'YWJj'

It's easy to simply take that output and decode() it, but my question is: what is a significance of base64.b64encode() returning bytes rather than a str?

解决方案

The purpose of the base64.b64encode() function is to convert binary data into ASCII-safe "text"

Python disagrees with that - base64 has been intentionally classified as a binary transform.

It was a design decision in Python 3 to force the separation of bytes and text and prohibit implicit transformations. Python is now so strict about this that bytes.encode doesn't even exist, and so b'abc'.encode('base64') would raise an AttributeError.

The opinion the language takes is that a bytestring object is already encoded. A codec which encodes bytes into text does not fit into this paradigm, because when you want to go from the bytes domain to the text domain it's a decode. Note that rot13 encoding was also banished from the list of standard encodings for the same reason - it didn't fit properly into the Python 3 paradigm.

There also can be a performance argument to make: suppose Python automatically handled decoding of the base64 output, which is an ASCII-encoded binary representation produced by C code from the binascii module, into a Python object in the text domain. If you actually wanted the bytes, you would just have to undo the decoding by encoding into ASCII again. It would be a wasteful round-trip, an unnecessary double-negation. Better to 'opt-in' for the decode-to-text step.

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