如何编写与 Python 2 和 Python 3 兼容的异常重新引发代码? [英] How to write exception reraising code that's compatible with both Python 2 and Python 3?

问题描述

我正在尝试使我的 WSGI 服务器实现与 Python 2 和 Python 3 兼容.我有以下代码:

I'm trying to make my WSGI server implementation compatible with both Python 2 and Python 3. I had this code:

def start_response(status, response_headers, exc_info = None):
    if exc_info:
        try:
            if headers_sent:
                # Re-raise original exception if headers sent.
                raise exc_info[0], exc_info[1], exc_info[2]
        finally:
            # Avoid dangling circular ref.
            exc_info = None
    elif headers_set:
        raise AssertionError("Headers already set!")

    headers_set[:] = [status, response_headers]
    return write

...相关部分是:

# Re-raise original exception if headers sent.
raise exc_info[0], exc_info[1], exc_info[2]

Python 3 不再支持该语法，因此必须将其转换为:

Python 3 doesn't support that syntax anymore so it must be translated to:

raise exc_info[0].with_traceback(exc_info[1], exc_info[2])

问题:Python 2 语法在 Python 3 中生成解析错误.如何编写可以被 Python 2 和 Python 3 解析的代码?我尝试了以下方法，但不起作用:

Problem: the Python 2 syntax generates a parse error in Python 3. How do I write code that can be parsed by both Python 2 and Python 3? I've tried the following, but that doesn't work:

if sys.version_info[0] >= 3:
    raise exc_info[0].with_traceback(exc_info[1], exc_info[2])
else:
    eval("raise exc_info[0], exc_info[1], exc_info[2]; 1", None, { 'exc_info': exc_info })

推荐答案

你可以做一些有创意的事情.

You could do something creative.

在代码的开头进行检查 - 您的构造函数或其他任何东西，检查您使用的 Python 版本，因为您的普通版本检查器不起作用，请尝试以下操作:

Have a check at the start of your code - your constructor or whatever, check what version of python you are using, since your normal version checker is not working, try this instead:

try:
  eval('a python 3 expression') # something that only works in python3+
  python_version = 3
except:
  python_version = 2

然后您的其余代码可以轻松地引用它以了解要使用的内容.

Then the rest of your code can easily just reference this to know what to use.

至于解析错误，你可以在函数中使用 exec，如下所示:

As for the parse errors, you can use exec in a function, like so:

def what_to_run():
    if python_version = 3:
        return 'raise exc_info[0].with_traceback(exc_info[1], exc_info[2])'
    else:
        return 'raise exc_info[0], exc_info[1], exc_info[2]'

在你的函数中你会这样写:

In your function you would write this:

def start_response(status, response_headers, exc_info = None):
    if exc_info:
        try:
            if headers_sent:
                # Re-raise original exception if headers sent.
                exec(what_to_run())
        finally:
            # Avoid dangling circular ref.
            exc_info = None
    elif headers_set:
        raise AssertionError("Headers already set!")

    headers_set[:] = [status, response_headers]
    return write

有点乱，未经测试，但它应该工作，至少你理解这个想法.

A bit messy, untested, but it should work, at least you understand the idea.

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