unicode_literals和type() [英] unicode_literals and type()

问题描述

我在type()调用上支持python2和python3时遇到问题.这说明了问题:

I'm having problems supporting python2 and python3 on a type() call. This demonstrates the problem:

from __future__ import unicode_literals

name='FooClass'
type(name, (dict,), {})

在python3上没有问题，但是在python2上:

No problem on python3, but on python2:

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    type(name, (dict,), {})
TypeError: type() argument 1 must be string, not unicode

这与在Python 2.6中使用unicode_literals的任何陷阱有关?.在该问题中，有人建议将类型转换为字节串，因此我天真地考虑使用 six.b() :

This is related to Any gotchas using unicode_literals in Python 2.6?. In that question, someone recommends typecasting to a bytestring, so naively I thought about using six.b():

假"字节文字.数据应始终为常规字符串文字. 在Python 2中，b()返回一个8位字符串.在Python 3中，数据已编码 将latin-1编码为字节.

A "fake" bytes literal. data should always be a normal string literal. In Python 2, b() returns a 8-bit string. In Python 3, data is encoded with the latin-1 encoding to bytes.

所以看起来像这样:

from __future__ import unicode_literals
import six

name='FooClass'
type(six.b(name), (dict,), {})

但是在python2和python3上均失败:

But it fails on both python2 and python3:

$ python2 test.py 
Traceback (most recent call last):
  File "test.py", line 6, in <module>
    type(six.b(name), (dict,), {})
TypeError: type() argument 1 must be string, not unicode

$ python3 test.py 
Traceback (most recent call last):
  File "test.py", line 6, in <module>
    type(six.b(name), (dict,), {})
TypeError: type() argument 1 must be str, not bytes

所以看来真的，type()想要一个python2 str，它是python2上的python3字节串，但是它想要一个python3 str，它是python3上的python2 unicode字符串.

So it seems that really, type() wants a python2 str which is a python3 bytestring on python2, but it wants a python3 str which is a python2 unicode string on python3.

您怎么看?

有什么我不理解的东西吗?

Is there something I don't understand ?

还是在python 2和3上与type()真正不兼容?

Or is there a real incompatibility with type() on python 2 and 3 ?

没有任何方法来进行相同的type()调用，同时支持2和3吗?

Isn't there any way to have the same type() call supporting both 2 and 3 ?

在这种情况下，像six这样的工具是否应该提供对type()的包装吗?

Shouldn't a tool like six provide a wrapper around type() in that case ?

推荐答案

six.b是在您不使用unicode_literals(并且将字符串文字作为文档传递给您)的前提下编写的状态)，因此Python 2实现只是def b(s): return s，因为Python 2字符串文字已经是字节字符串.

six.b is written under the assumption that you won't use unicode_literals (and that you'll pass a string literal to it, as the documentation states), so the Python 2 implementation is just def b(s): return s as a Python 2 string literal is already a byte string.

在此模块中不要使用unicode_literals，或使用(如注释所示)str(name).在Python 3中，这是无操作的.在Python 2中，它无声地将unicode字符串转换为字节字符串(假设有些编码我不介意记住，但是它是ASCII的超集，所以应该没问题).

Either don't use unicode_literals in this module, or use (as a comment suggests) str(name). In Python 3, that is a no-op. In Python 2, it silently converts the unicode string to a byte string (assuming some encoding that I can't be bothered to remember, but it's a superset of ASCII so you should be fine).

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