在将字符串强制转换为 unicode 时，如何让 python 2.x 发出警告? [英] How can you make python 2.x warn when coercing strings to unicode?

问题描述

编码错误的一个非常常见的来源是，当您将字符串与 unicode 一起添加时，python 2 会默默地将字符串强制转换为 unicode.这会导致混合编码问题并且很难调试.

A very common source of encoding errors is that python 2 will silently coerce strings to unicode when you add them together with unicode. This can cause mixed encoding problems and can be very hard to debug.

例如:

import urllib
import webbrowser
name = raw_input("What's your name?\nName: ")
greeting = "Hello, %s" % name
if name == "John":
    greeting += u' (Feliz cumplea\xf1os!)'
webbrowser.open('http://lmgtf\x79.com?q=' + urllib.quote_plus(greeting))

如果您输入John"，将会失败并显示一个神秘的错误:

will fail with a cryptic error if you enter "John":

/usr/lib/python2.7/urllib.py:1268: UnicodeWarning: Unicode equal comparison faile
d to convert both arguments to Unicode - interpreting them as being unequal
  return ''.join(map(quoter, s))
Traceback (most recent call last):
  File "feliz.py", line 7, in <module>
    webbrowser.open('http://lmgtf\x79.com?q=' + urllib.quote_plus(greeting))
  File "/usr/lib/python2.7/urllib.py", line 1273, in quote_plus
    s = quote(s, safe + ' ')
  File "/usr/lib/python2.7/urllib.py", line 1268, in quote
    return ''.join(map(quoter, s))
KeyError: u'\xf1'

当实际错误远离实际强制发生的地方时，特别难以追踪.

It's particularly hard to track down when the actual errors come far down the road from where the actual coercion happened.

如何配置python在字符串被强制为unicode时立即给出警告或异常?

How can you configure python to give a warning or exception immediately when strings are coerced to unicode?

推荐答案

在提出这个问题后，我做了更多的研究并找到了完美的答案.Armin Ronacher 创建了一个很棒的小工具，名为 unicode-nazi.只需安装它并像这样运行你的程序:

I did a little more research after asking this question and hit on the perfect answer. Armin Ronacher created a wonderful little tool called unicode-nazi. Just install it and run your program like this:

python -Werror -municodenazi myprog.py

你会在强制发生的地方得到回溯:

and you get a traceback right where the coercion happened:

Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "SITE-PACKAGES/unicodenazi.py", line 128, in <module>
    main()
  File "SITE-PACKAGES/unicodenazi.py", line 119, in main
    execfile(sys.argv[0], main_mod.__dict__)
  File "myprog.py", line 4, in <module>
    print foo()
  File "myprog.py", line 2, in foo
    return 'bar' + u'baz'
  File "SITE-PACKAGES/unicodenazi.py", line 34, in warning_decode
    stacklevel=2)
UnicodeWarning: Implicit conversion of str to unicode

<小时>

如果您正在处理本身会触发隐式强制转换的 Python 库，并且您无法捕获异常或以其他方式解决它们，则可以省略 -Werror:

python -municodenazi myprog.py

并且至少在它发生时看到在 stderr 上打印的警告:

and at least see a warning printed out on stderr when it happens:

/SITE-PACKAGES/unicodenazi.py:119: UnicodeWarning: Implicit conversion of str to unicode
  execfile(sys.argv[0], main_mod.__dict__)
barbaz

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