Python：从 ISO-8859-1/latin1 转换为 UTF-8

Question

I have this string that has been decoded from Quoted-printable to ISO-8859-1 with the email module. This gives me strings like "\xC4pple" which would correspond to "Äpple" (Apple in Swedish). However, I can't convert those strings to UTF-8.

>>> apple = "\xC4pple"
>>> apple
'\xc4pple'
>>> apple.encode("UTF-8")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc4 in position 0: ordinal not in     range(128)

What should I do?

Answer 1

This is a common problem, so here's a relatively thorough illustration.

For non-unicode strings (ie those without u prefix like u'\xc4pple' ), one must decode from the native encoding ( iso8859-1 / latin1 , unless modified with the enigmatic sys.setdefaultencoding function) to unicode , then encode to a character set that can display the characters you wish, in this case I'd recommend UTF-8 .

First, here is a handy utility function that'll help illuminate the patterns of Python 2.7 string and unicode:

>>> def tell_me_about(s): return (type(s), s)

A plain string

>>> v = "\xC4pple" # iso-8859-1 aka latin1 encoded string

>>> tell_me_about(v)
(<type 'str'>, '\xc4pple')

>>> v
'\xc4pple'        # representation in memory

>>> print v
?pple             # map the iso-8859-1 in-memory to iso-8859-1 chars
                  # note that '\xc4' has no representation in iso-8859-1, 
                  # so is printed as "?".

Decoding a iso8859-1 string - convert plain string to unicode

>>> uv = v.decode("iso-8859-1")
>>> uv
u'\xc4pple'       # decoding iso-8859-1 becomes unicode, in memory

>>> tell_me_about(uv)
(<type 'unicode'>, u'\xc4pple')

>>> print v.decode("iso-8859-1")
Äpple             # convert unicode to the default character set
                  # (utf-8, based on sys.stdout.encoding)

>>> v.decode('iso-8859-1') == u'\xc4pple'
True              # one could have just used a unicode representation 
                  # from the start

A little more illustration — with “Ä”

>>> u"Ä" == u"\xc4"
True              # the native unicode char and escaped versions are the same

>>> "Ä" == u"\xc4"  
False             # the native unicode char is '\xc3\x84' in latin1

>>> "Ä".decode('utf8') == u"\xc4"
True              # one can decode the string to get unicode

>>> "Ä" == "\xc4"
False             # the native character and the escaped string are
                  # of course not equal ('\xc3\x84' != '\xc4').

Encoding to UTF

>>> u8 = v.decode("iso-8859-1").encode("utf-8")
>>> u8
'\xc3\x84pple'    # convert iso-8859-1 to unicode to utf-8

>>> tell_me_about(u8)
(<type 'str'>, '\xc3\x84pple')

>>> u16 = v.decode('iso-8859-1').encode('utf-16')
>>> tell_me_about(u16)
(<type 'str'>, '\xff\xfe\xc4\x00p\x00p\x00l\x00e\x00')

>>> tell_me_about(u8.decode('utf8'))
(<type 'unicode'>, u'\xc4pple')

>>> tell_me_about(u16.decode('utf16'))
(<type 'unicode'>, u'\xc4pple')

Relationship between unicode and UTF and latin1

>>> print u8
Äpple             # printing utf-8 - because of the encoding we now know
                  # how to print the characters

>>> print u8.decode('utf-8') # printing unicode
Äpple

>>> print u16     # printing 'bytes' of u16
���pple

>>> print u16.decode('utf16')
Äpple             # printing unicode

>>> v == u8
False             # v is a iso8859-1 string; u8 is a utf-8 string

>>> v.decode('iso8859-1') == u8
False             # v.decode(...) returns unicode

>>> u8.decode('utf-8') == v.decode('latin1') == u16.decode('utf-16')
True              # all decode to the same unicode memory representation
                  # (latin1 is iso-8859-1)

Unicode Exceptions

 >>> u8.encode('iso8859-1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 0:
  ordinal not in range(128)

>>> u16.encode('iso8859-1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xff in position 0:
  ordinal not in range(128)

>>> v.encode('iso8859-1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc4 in position 0:
  ordinal not in range(128)

One would get around these by converting from the specific encoding (latin-1, utf8, utf16) to unicode eg u8.decode('utf8').encode('latin1') .

So perhaps one could draw the following principles and generalizations:

• a type str is a set of bytes, which may have one of a number of encodings such as Latin-1, UTF-8, and UTF-16
• a type unicode is a set of bytes that can be converted to any number of encodings, most commonly UTF-8 and latin-1 (iso8859-1)
• the print command has its own logic for encoding , set to sys.stdout.encoding and defaulting to UTF-8
• One must decode a str to unicode before converting to another encoding.

Of course, all of this changes in Python 3.x.

Hope that is illuminating.

Further reading

• Characters vs. Bytes , by Tim Bray.

And the very illustrative rants by Armin Ronacher:

• The Updated Guide to Unicode on Python (July 2, 2013)
• More About Unicode in Python 2 and 3 (January 5, 2014)
• UCS vs UTF-8 as Internal String Encoding (January 9, 2014)
• Everything you did not want to know about Unicode in Python 3 (May 12, 2014)

Answer 2

Try decoding it first, then encoding:

apple.decode('iso-8859-1').encode('utf8')

Answer 3

For Python 3:

bytes(apple,'iso-8859-1').decode('utf-8')

I used this for a text incorrectly encoded as iso-8859-1 (showing words like VeÅ\x99ejné ) instead of utf-8. This code produces correct version Veřejné .

Answer 4

Decode to Unicode, encode the results to UTF8.

apple.decode('latin1').encode('utf8')

Answer 5

concept = concept.encode('ascii', 'ignore') 
concept = MySQLdb.escape_string(concept.decode('latin1').encode('utf8').rstrip())

I do this, I am not sure if that is a good approach but it works everytime !!