Python urllib.unquote defect

Python 2.5 Win32

The unquote function of Python standard module urllib performs percent decoding. According to RFC, percent encoded string is case insensitive, which means %CE, %ce, %cE and %Ce are equivalent. urllib.unquote is, however, unable to process the mixed case properly.

urllib.unquote(‘%cE’) # -> ‘%cE’
urllib.unquote(‘%Ce’) # -> ‘%Ce’

But the correct result should be ‘\xce’. Why doesn’t unquote forgive the mixed case? I had a look at the implementation.

_hextochr = dict(('%02x' % i, chr(i)) for i in range(256))
_hextochr.update(('%02X' % i, chr(i)) for i in range(256))

def unquote(s):
    """unquote('abc%20def') -> 'abc def'."""
    res = s.split('%')
    for i in xrange(1, len(res)):
        item = res[i]
        try:
            res[i] = _hextochr[item[:2]] + item[2:]
        except KeyError:
            res[i] = '%' + item
        except UnicodeDecodeError:
            res[i] = unichr(int(item[:2], 16)) + item[2:]
    return "".join(res)

The _hextochr dictionary contains lower cased keys and upper cased keys but no mixed cased keys.

A work around : res[i] = _hextochr[item[:2].upper()] + item[2:]

UPDATE 2006-11-17 23:10:14 GMT+0800

In urllib.py

always_safe = ('ABCDEFGHIJKLMNOPQRSTUVWXYZ'
               'abcdefghijklmnopqrstuvwxyz'
               '0123456789' '_.-')
But according to RFC2396 all unreserved characters are safe, so the always_safe sequence should also include '~'.
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