Python – Bytes in a unicode Python string

character-encodingpythonunicodeutf-8

In Python 2, Unicode strings may contain both unicode and bytes:

a = u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \xd0\xb5\xd0\xba'

I understand that this is absolutely not something one should write in his own code, but this is a string that I have to deal with.

The bytes in the string above are UTF-8 for ек (Unicode \u0435\u043a).

My objective is to get a unicode string containing everything in Unicode, which is to say Русский ек (\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \u0435\u043a).

Encoding it to UTF-8 yields

>>> a.encode('utf-8')
'\xd0\xa0\xd1\x83\xd1\x81\xd1\x81\xd0\xba\xd0\xb8\xd0\xb9 \xc3\x90\xc2\xb5\xc3\x90\xc2\xba'

Which then decoded from UTF-8 gives the initial string with bytes in them, which is not good:

>>> a.encode('utf-8').decode('utf-8')
u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \xd0\xb5\xd0\xba'

I found a hacky way to solve the problem, however:

>>> repr(a)
"u'\\u0420\\u0443\\u0441\\u0441\\u043a\\u0438\\u0439 \\xd0\\xb5\\xd0\\xba'"
>>> eval(repr(a)[1:])
'\\u0420\\u0443\\u0441\\u0441\\u043a\\u0438\\u0439 \xd0\xb5\xd0\xba'
>>> s = eval(repr(a)[1:]).decode('utf8')
>>> s
u'\\u0420\\u0443\\u0441\\u0441\\u043a\\u0438\\u0439 \u0435\u043a'
# Almost there, the bytes are proper now but the former real-unicode characters
# are now escaped with \u's; need to un-escape them.
>>> import re
>>> re.sub(u'\\\\u([a-f\\d]+)', lambda x : unichr(int(x.group(1), 16)), s)
u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \u0435\u043a' # Success!

This works fine but looks very hacky due to its use of eval, repr, and then additional regex'ing of the unicode string representation. Is there a cleaner way?

Best Solution

In Python 2, Unicode strings may contain both unicode and bytes:

No, they may not. They contain Unicode characters.

Within the original string, \xd0 is not a byte that's part of a UTF-8 encoding. It is the Unicode character with code point 208. u'\xd0' == u'\u00d0'. It just happens that the repr for Unicode strings in Python 2 prefers to represent characters with \x escapes where possible (i.e. code points < 256).

There is no way to look at the string and tell that the \xd0 byte is supposed to be part of some UTF-8 encoded character, or if it actually stands for that Unicode character by itself.

However, if you assume that you can always interpret those values as encoded ones, you could try writing something that analyzes each character in turn (use ord to convert to a code-point integer), decodes characters < 256 as UTF-8, and passes characters >= 256 as they were.