CODEWITHSUNDEEP
pythonunicodeutf-8
Morten Siebuhr
Morten Siebuhr

Reputation: 6108

Double-decoding unicode in python

I am working against an application that seems keen on returning, what I believe to be, double UTF-8 encoded strings.

I send the string u'XüYß' encoded using UTF-8, thus becoming X\u00fcY\u00df (equal to X\xc3\xbcY\xc3\x9f).

The server should simply echo what I sent it, yet returns the following: X\xc3\x83\xc2\xbcY\xc3\x83\xc2\x9f (should be X\xc3\xbcY\xc3\x9f). If I decode it using str.decode('utf-8') becomes u'X\xc3\xbcY\xc3\x9f', which looks like a ... unicode-string, containing the original string encoded using UTF-8.

But Python won't let me decode a unicode string without re-encoding it first - which fails for some reason, that escapes me:

>>> ret = 'X\xc3\x83\xc2\xbcY\xc3\x83\xc2\x9f'.decode('utf-8')
>>> ret
u'X\xc3\xbcY\xc3\x9f'
>>> ret.decode('utf-8')
# Throws UnicodeEncodeError: 'ascii' codec can't encode ...

How do I persuade Python to re-decode the string? - and/or is there any (practical) way of debugging what's actually in the strings, without passing it though all the implicit conversion print uses?

(And yes, I have reported this behaviour with the developers of the server-side.)

Upvotes: 17

Views: 15755

Answers (4)

user3850
user3850

Reputation:

ret.decode() tries implicitly to encode ret with the system encoding - in your case ascii.

If you explicitly encode the unicode string, you should be fine. There is a builtin encoding that does what you need:

>>> 'X\xc3\xbcY\xc3\x9f'.encode('raw_unicode_escape').decode('utf-8')
'XüYß'

Really, .encode('latin1') (or cp1252) would be OK, because that's what the server is almost cerainly using. The raw_unicode_escape codec will just give you something recognizable at the end instead of raising an exception:

>>> '€\xe2\x82\xac'.encode('raw_unicode_escape').decode('utf8')
'\\u20ac€'

>>> '€\xe2\x82\xac'.encode('latin1').decode('utf8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'latin-1' codec can't encode character '\u20ac' in position 0: ordinal not in range(256)

In case you run into this sort of mixed data, you can use the codec again, to normalize everything:

>>> '€\xe2\x82\xac'.encode('raw_unicode_escape').decode('utf8')
'\\u20ac€'

>>> '\\u20ac€'.encode('raw_unicode_escape')
b'\\u20ac\\u20ac'
>>> '\\u20ac€'.encode('raw_unicode_escape').decode('raw_unicode_escape')
'€€'

Upvotes: 29

s29
s29

Reputation: 2057

Here's a little script that might help you, doubledecode.py -- https://gist.github.com/1282752

Upvotes: 0

Chris Morgan
Chris Morgan

Reputation: 90722

Don't use this! Use @hop's solution.

My nasty hack: (cringe! but quietly. It's not my fault, it's the server developers' fault)

def double_decode_unicode(s, encoding='utf-8'):
    return ''.join(chr(ord(c)) for c in s.decode(encoding)).decode(encoding)

Then,

>>> double_decode_unicode('X\xc3\x83\xc2\xbcY\xc3\x83\xc2\x9f')
u'X\xfcY\xdf'
>>> print _
XüYß

Upvotes: 0

u0b34a0f6ae
u0b34a0f6ae

Reputation: 49793

What you want is the encoding where Unicode code point X is encoded to the same byte value X. For code points inside 0-255 you have this in the latin-1 encoding:

def double_decode(bstr):
    return bstr.decode("utf-8").encode("latin-1").decode("utf-8")

Upvotes: 3

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