在强制字符串转换为unicode时,如何让python 2.x发出警告?

编码错误的一个非常常见的来源是,当你将字符串与unicode一起添加时,python 2会默默地将字符串强制转换为unicode.这可能会导致混合编码问题,并且可能很难调试.

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))

如果输入“John”,将会出现神秘错误:

/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'

当实际的强制发生时,实际的错误发生在远离道路的地方,特别难以追查.

当字符串被强制转换为unicode时,如何配置python以立即发出警告或异常?

最佳答案
在提出这个问题后,我做了一些研究并找到了完美的答案. Armin Ronacher创建了一个名为unicode-nazi的精彩小工具.只需安装它并像这样运行你的程序:

python -Werror -municodenazi myprog.py

并且你会在强制发生的地方得到追溯:

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

如果您正在处理自己触发隐式强制的python库,并且您无法捕获异常或以其他方式解决它们,您可以省略-Werror:

python -municodenazi myprog.py

并且当它发生时至少看到stderr上打印出的警告:

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

转载注明原文:在强制字符串转换为unicode时,如何让python 2.x发出警告? - 代码日志