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I’ve never been sure that I understand the difference between str/unicode decode and encode.
I know that str().decode() is for when you have a string of bytes that you know has a certain character encoding, given that encoding name it will return a unicode string.
I know that unicode().encode() converts unicode chars into a string of bytes according to a given encoding name.
But I don’t understand what str().encode() and unicode().decode() are for. Can anyone explain, and possibly also correct anything else I’ve gotten wrong above?
EDIT:
Several answers give info on what .encode does on a string, but no-one seems to know what .decode does for unicode.
解决方案
The decode method of unicode strings really doesn’t have any applications at all (unless you have some non-text data in a unicode string for some reason — see below). It is mainly there for historical reasons, i think. In Python 3 it is completely gone.
unicode().decode() will perform an implicit encoding of s using the default (ascii) codec. Verify this like so:
>>> s = u’ö’
>>> s.decode()
Traceback (most recent call last):
File “”, line 1, in
UnicodeEncodeError: ‘ascii’ codec can’t encode character u’\xf6′ in position 0:
ordinal not in range(128)
>>> s.encode(‘ascii’)
Traceback (most recent call last):
File “”, line 1, in
UnicodeEncodeError: ‘ascii’ codec can’t encode character u’\xf6′ in position 0:
ordinal not in range(128)
The error messages are exactly the same.
For str().encode() it’s the other way around — it attempts an implicit decoding of s with the default encoding:
>>> s = ‘ö’
>>> s.decode(‘utf-8’)
u’\xf6′
>>> s.encode()
Traceback (most recent call last):
File “”, line 1, in
UnicodeDecodeError: ‘ascii’ codec can’t decode byte 0xc3 in position 0:
ordinal not in range(128)
Used like this, str().encode() is also superfluous.
But there is another application of the latter method that is useful: there are encodings that have nothing to do with character sets, and thus can be applied to 8-bit strings in a meaningful way:
>>> s.encode(‘zip’)
‘x\x9c;\xbc\r\x00\x02>\x01z’
You are right, though: the ambiguous usage of “encoding” for both these applications is… awkard. Again, with separate byte and string types in Python 3, this is no longer an issue.
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