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Representing non-English characters with Unicode (UTF-8)

I am working with an HTML string in Python that contains non-English characters that is represented in the string by 16-bit unicode hex values. The string reads:
"Skr\u00E4ddarev\u00E4gen"
The string when properly converted should read "Skräddarevägen". How do i ensure that the unicode hex value gets correctly encoded/decoded on output and reads with the correct accents?
(Note, I'm using Requests and Pandas and the encoding in both is set to utf-8)
Thanks in advance!

In Python 3, the following can happen:
If you pick up your string from an HTML file, you have to read in
the HTML file using the correct encoding.
If you have your string in Python 3 code, it should be already in Unicode (32-bit) in memory.
Write the string out to a file, you have to specify the encoding you want in the file open.

If you are using Python 3 and that is literally the content of the string, it "just works":
>>> s = "Skr\u00E4ddarev\u00E4gen"
>>> s
'Skräddarevägen'
If you have that string as raw data, you have to decode it. If it is a Unicode string you'll have to encode it to bytes first. The final result will be Unicode. If you already have a byte string, skip the encode step.
>>> s = r"Skr\u00E4ddarev\u00E4gen"
>>> s
'Skr\\u00E4ddarev\\u00E4gen'
>>> s.encode('ascii').decode('unicode_escape')
'Skräddarevägen'
If you are on Python 2, you'll need to decode, plus print to see it properly:
>>> s = "Skr\u00E4ddarev\u00E4gen"
>>> s
'Skr\\u00E4ddarev\\u00E4gen'
>>> s.decode('unicode_escape')
u'Skr\xe4ddarev\xe4gen'
>>> print s.decode('unicode_escape')
Skräddarevägen

From your display, it is hard to be sure what is in the string. Assuming that it is the 24 characters displayed, I believe the last line of the following answers your question.
s = "Skr\\u00E4ddarev\\u00E4gen"
print(len(s))
for c in s: print(c, end=' ')
print()
print(eval("'"+s+"'"))
print(eval("'"+s+"'").encode('utf-8'))
This prints
24
S k r \ u 0 0 E 4 d d a r e v \ u 0 0 E 4 g e n
Skräddarevägen
b'Skr\xc3\xa4ddarev\xc3\xa4gen'

python write file dealing with encode

I'm confused. I need HELP!!!
I'm dealing with a file contains Chinese characters,for instance, let's call it a.TEST, and here is what's inside.
你好 中国 Hello China 1 2 3
You don't need to understand what the chinese means.(Actually it's 'hello China')
>>> f=open('wr.TRAIN')
>>> print f.read()
你好 中国 Hello China 1 2 3
>>> f.seek(0)
>>> content = f.readline()
>>> content
'\xe4\xbd\xa0\xe5\xa5\xbd \xe4\xb8\xad\xe5\x9b\xbd Hello China 1 2 3\n'
>>> print content
你好 中国 Hello China 1 2 3
>>> type(content)
<type 'str'>
>>> isinstance(content,unicode)
False
Here comes the first Question: Why python shell give me the utf-8of content when i just type content,meanwhile print content cmd can output the form that I want to see?
The Second Question: what's the difference between unicode and str?
Someone told me that encode is convert unicode to str, but what i learned from Unicode HowTo tells me encode is convert unicode to utf-8
Not over yet! :)
here is test.py
#!/usr/bin/python
#-*- coding: utf-8 -*-
fr = open('a.TEST')
fw = open('out.TEST','w')
content = fr.readline()
content_list = content.split()
print content
fw.write('{0}'.format(content_list))
fr.close()
fw.close()
Third Question:Why the chinese character turn into utf-8 code when I do .split()?
and I thought fw.write('{0}'.format(content_list).decode('utf-8')) will work, but it doesn't.
I don't want what's written into out.TEST is character encoding form, I want it to be exactly the character that look like originally（你好）. How to do it?

What is Encoding
A file consists of bytes. You can represent each byte with a number between 0 and 255 (or 0x00 and 0xFF in hexadecimal).
Text is also written as bytes. There is an agreement on the way text is written. That is an encoding. The most basic encoding is ASCII and other encodings are usually based on it. For example, ASCII defines that number 65 (0x41) represents 'A', 66 (0x42) represents 'B' etc.
How are Strings Represented
In python, you can define a string using numeric values:
>>> '\x41\x42\x43'
'ABC'
'\x41\x42\x43' is exactly the same thing as 'ABC'. Python will always represent the string using the more readable textual representation ('ABC').
However, some numeric values are not printable characters, so they will be represented in numeric form:
>>> '\x00\x01\x02\x03\x04'
'\x00\x01\x02\x03\x04'
Others characters have aliases to make your job easier:
>>> '\x0a\x0d\x09'
'\n\r\t'
Different Encodings
ASCII table defines meaning of numbers 0-127 and includes only the english alphabet. Numbers 128-255 are undefined. So, other encodings define a meaning for 128-255. Yet others change the meaning of the whole range 0-255.
There are many encodings and they define 128-255 differently.
For example, character 185 (0xB9) is ą in windows-1250 encoding, but it is š in iso-8859-2 encoding.
So, what happens if you print \xb9? It depends on the encoding used in the console. In my case (my console uses cp852 encoding) it is:
>>> print '\xb9'
╣
Because of that ambiguity, string '\xb9' will never be represented as '╣' (nor 'ą'...). That would hide the true value. It will be represented as the numeric value:
>>> '\xb9'
'\xb9'
Also:
>>> '╣'
'\xb9'
See also the string from the question in my console:
>>> content = '\xe4\xbd\xa0\xe5\xa5\xbd \xe4\xb8\xad\xe5\x9b\xbd Hello China 1 2 3\n'
>>>
>>> content
'\xe4\xbd\xa0\xe5\xa5\xbd \xe4\xb8\xad\xe5\x9b\xbd Hello China 1 2 3\n'
>>>
>>> print content
ńŻáňąŻ ńŞşňŤŻ Hello China 1 2 3
But what happens if variable is just entered in the console?
When a variable is enteren in cosole without print, its representation is printed. It is the same as the following:
>>> print repr(content)
'\xe4\xbd\xa0\xe5\xa5\xbd \xe4\xb8\xad\xe5\x9b\xbd Hello China 1 2 3\n'
What is Unicode?
Unicode table aims to define a numeric representation of all characters in the world and more. It can actually do that, because it is not limited to 256 values (or to any other limit actually). This is not an encoding, but a universal mapping of numbers to characters.
For example, unicode defines that number 353 (0x0161) is character š. That is allways true regardless of your locale and encodings you use. That character can be stored in files (or memory) in any encoding which supports š.
What is UTF-8?
When encoding a unicode character, one can use any encoding, but not all of them will support all characters.
For example, š (unicode 0x0161) can be encoded in iso-8869-2 as 0xB9, but it cannot be encoded in iso-8869-1 at all.
So, to be able to encode anything, you need an encoding which supports every unicode character. UTF-8 is one of those encodings, but there are others:
>>> u'\u0161'.encode('utf-7')
'+AWE-'
>>> u'\u0161'.encode('utf-8')
'\xc5\xa1'
>>> u'\u0161'.encode('utf-16le')
'a\x01'
>>> u'\u0161'.encode('utf-16be')
'\x01a'
>>> u'\u0161'.encode('utf-32le')
'a\x01\x00\x00'
>>> u'\u0161'.encode('utf-32be')
'\x00\x00\x01a'
The good thing about utf-8 is that the whole ASCII range is unchanged and as long as only ASCII is used, only one byte is used per character:
>>> u'abcdefg'.encode('utf-8')
'abcdefg'
Unicode in Python 2
Important: This is really specific to Python 2. Python 3 is different.
Unlike str objects, which are strings of bytes, unicode objects are strings of unicode characters.
They can be encoded into a str in chosen encoding, or decoded from str in chosen encoding.
A unicode string is specified using u before the opening quote. The characters inside are interpreted using current encoding, or they can be specified in numeric format \uHEX:
>>> u'ABCD'
u'ABCD'
>>>
>>> u'\u0041\u0042\u0043'
u'ABC'
>>> u'šâů'
u'\u0161\xe2\u016f'
And Now the Answers
First Question
contents prints repr(contents)
print contents prints contents
Second Question
UTF-8 strings are byte strings (str). You get them by encoding the unicode:
>>> u'\u0161'.encode('utf-8')
'\xc5\xa1'
>>> '\xc5\xa1'.decode('utf-8')
u'\u0161'
So yes, encode converts unicode to str. The str can be utf-8, but it does not have to be.
Third Question
A) "Why the chinese character turn into utf-8 code when I do .split()?"
They were utf-8 all the time.
B) "I thought fw.write('{0}'.format(content_list).decode('utf-8')) will work"
content_list is not a string. It is a list. When a list is converted to a string, it is done using its repr, which also does repr of all of the contents.
For example:
>>> 'a \n a \n a'
'a \n a \n a'
>>> print 'a \n a \n a'
a
a
a
>>> print ['a \n a \n a']
['a \n a \n a']
The last print printed repr(list) which contains repr(str).

In the beginning, there was just english characters, and people was not satisfied.
Then they want to display every character in the world.But there is problem. One byte can only represent 255 characters. There just simply not enough place to hold them.
Then people decide to use two byte to represent one character.And call it 'utf8'.
No matter what characters you write in, it's all store in byte form.
In Python, there is no such datatype called 'unicode', just 'str'. And 'unicode' is an encoding system of 'str'.
'\xe4\xbd\xa0\xe5\xa5\xbd \xe4\xb8\xad\xe5\x9b\xbd' is byte form of "你好 中国".
It can not display without an encoding system specified.
I suppose you could blame linux/unix. Python has no problem to display 'utf-8' characters, while 'cat' cannot.

string.decode() function in python2

So I am converting some code from python2 to python3. I don't understand the python2 encode/decode functionality enough to even determine what I should be doing in python3
In python2, I can do the following things:
>>> c = '\xe5\xb8\x90\xe6\x88\xb7'
>>> print c
帐户
>>> c.decode('utf8')
u'\u5e10\u6237'
What did I just do there? Doesn't the 'u' prefix mean unicode? Shouldn't the utf8 be '\xe5\xb8\x90\xe6\x88\xb7' since that is what I input in the first place?

Your variable c was not declared as a unicode (with prefix 'u'). If you decode it using the 'latin1' encoding you will get the same result:
>>> c.decode('latin1')
u'\xe5\xb8\x90\xe6\x88\xb7'
Note that the result of decode is a unicode string:
>>> type(c)
<type 'str'>
>>> type(c.decode('latin1'))
<type 'unicode'>
If you declare c as a unicode and keep the same input, you will not print the same characters:
>>> c=u'\xe5\xb8\x90\xe6\x88\xb7'
>>> print c
å¸æ·
If you use the input '\u5e10\u6237', you will print the initial characters:
>>> c=u'\u5e10\u6237'
>>> print c
帐户
Encoding and decoding is just a matter of using a table of correspondence value<->character. The thing is that the same value does not render the same character according to the encoding (ie table) used.
The main difficulty is when you don't know the encoding of an input string that you have to handle. Some tools can try to guess it, but it is not always successful (see https://superuser.com/questions/301552/how-to-auto-detect-text-file-encoding).

How do you decode an ascii string in python?

For example, in your python shell(IDLE):
>>> a = "\x3cdiv\x3e"
>>> print a
The result you get is:
<div>
but if a is an ascii encoded string:
>>> a = "\\x3cdiv\\x3e" ## it's the actual \x3cdiv\x3e string if you read it from a file
>>> print a
The result you get is:
\x3cdiv\x3e
Now what i really want from a is <div>, so I did this:
>>> b = a.decode("ascii")
>>> print b
BUT surprisingly I did NOT get the result I want, it's still:
\x3cdiv\x3e
So basically what do I do to convert a, which is \x3cdiv\x3e to b, which should be <div>?
Thanks

>>> a = rb"\x3cdiv\x3e"
>>> a.decode('unicode_escape')
'<div>'
Also check out some interesting codecs.

With python 3.x, you would adapt Kabie answer to
a = b"\x3cdiv\x3e"
a.decode('unicode_escape')
or
a = b"\x3cdiv\x3e"
a.decode('ascii')
both give
>>> a
b'<div>'
What is b prefix for ?
Bytes literals are always prefixed with 'b' or 'B'; they produce an
instance of the bytes type instead of the str type. They may only
contain ASCII characters; bytes with a numeric value of 128 or greater
must be expressed with escapes.

Bytes in a unicode Python string

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?

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.

(In response to the comments above): this code converts everything that looks like utf8 and leaves other codepoints as is:
a = u'\u0420\u0443\u0441 utf:\xd0\xb5\xd0\xba bytes:bl\xe4\xe4'
def convert(s):
try:
return s.group(0).encode('latin1').decode('utf8')
except:
return s.group(0)
import re
a = re.sub(r'[\x80-\xFF]+', convert, a)
print a.encode('utf8')
Result:
Рус utf:ек bytes:blää

The problem is that your string is not actually encoded in a specific encoding. Your example string:
a = u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \xd0\xb5\xd0\xba'
Is mixing python's internal representation of unicode strings with utf-8 encoded text. If we just consider the 'special' characters:
>>> orig = u'\u0435\u043a'
>>> bytes = u'\xd0\xb5\xd0\xba'
>>> print orig
ек
>>> print bytes
ек
But you say, bytes is utf-8 encoded:
>>> print bytes.encode('utf-8')
ек
>>> print bytes.encode('utf-8').decode('utf-8')
ек
Wrong! But what about:
>>> bytes = '\xd0\xb5\xd0\xba'
>>> print bytes
ек
>>> print bytes.decode('utf-8')
ек
Hurrah.
So. What does this mean for me? It means you're (probably) solving the wrong problem. What you should be asking us/trying to figure out is why your strings are in this form to begin with and how to avoid it/fix it before you have them all mixed up.

You should convert unichrs to chrs, then decode them.
u'\xd0' == u'\u00d0' is True
$ python
>>> import re
>>> a = u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \xd0\xb5\xd0\xba'
>>> re.sub(r'[\000-\377]*', lambda m:''.join([chr(ord(i)) for i in m.group(0)]).decode('utf8'), a)
u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \u0435\u043a'
r'[\000-\377]*' will match unichrs u'[\u0000-\u00ff]*'
u'\xd0\xb5\xd0\xba' == u'\u00d0\u00b5\u00d0\u00ba'
You use utf8 encoded bytes as unicode code points (this is the PROBLEM)
I solve the problem by pretending those mistaken unichars as the corresponding bytes
I search all these mistaken unichars, and convert them to chars, then decode them.
If I'm wrong, please tell me.

You've already got an answer, but here's a way to unscramble UTF-8-like Unicode sequences that is less likely to decode latin-1 Unicode sequences in error. The re.sub function:
Matches Unicode characters < U+0100 that resemble valid UTF-8 sequences (ref: RFC 3629).
Encodes the Unicode sequence into its equivalent latin-1 byte sequence.
Decodes the sequence using UTF-8 back into Unicode.
Replaces the original UTF-8-like sequence with the matching Unicode character.
Note this could still match a Unicode sequence if just the right characters appear next to each other, but it is much less likely.
import re
# your example
a = u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \xd0\xb5\xd0\xba'
# printable Unicode characters < 256.
a += ''.join(chr(n) for n in range(32,256)).decode('latin1')
# a few UTF-8 characters decoded as latin1.
a += ''.join(unichr(n) for n in [2**7-1,2**7,2**11-1,2**11]).encode('utf8').decode('latin1')
# Some non-BMP characters
a += u'\U00010000\U0010FFFF'.encode('utf8').decode('latin1')
print repr(a)
# Unicode codepoint sequences that resemble UTF-8 sequences.
p = re.compile(ur'''(?x)
\xF0[\x90-\xBF][\x80-\xBF]{2} | # Valid 4-byte sequences
[\xF1-\xF3][\x80-\xBF]{3} |
\xF4[\x80-\x8F][\x80-\xBF]{2} |
\xE0[\xA0-\xBF][\x80-\xBF] | # Valid 3-byte sequences
[\xE1-\xEC][\x80-\xBF]{2} |
\xED[\x80-\x9F][\x80-\xBF] |
[\xEE-\xEF][\x80-\xBF]{2} |
[\xC2-\xDF][\x80-\xBF] # Valid 2-byte sequences
''')
def replace(m):
return m.group(0).encode('latin1').decode('utf8')
print
print repr(p.sub(replace,a))
###Output
u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \xd0\xb5\xd0\xba
!"#$%&'()*+,-./0123456789:;<=>?#ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff\x7f\xc2\x80\xdf\xbf\xe0\xa0\x80\xf0\x90\x80\x80\xf4\x8f\xbf\xbf'
u'\u0420\u0443\u0441\u0441\u043a\u0438\u0439 \u0435\u043a
!"#$%&'()*+,-./0123456789:;<=>?#ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff\x7f\x80\u07ff\u0800\U00010000\U0010ffff'

I solved it by
unicodeText.encode("utf-8").decode("unicode-escape").encode("latin1")