Another thing which has been on my stack for quite a while has been a unicode doctest howto, as I remember I was quite lost when I first tried to test encoding stuff in a doctest.
So I thought the ultimate way to show how to do this would be in a doctest 😉
# -*- coding: utf-8 -*- def testDocTestUnicode(): ur"""Non ascii letters in doctests actually are tricky. The reason why things work here that usually don't (each marked with a #BAD!) is explained quite in the end of this doctest, but the essence is: we didn't only fix the encoding of this file, but also the sys.defaultencoding, which you should never do. This file has a utf8 input encoding, which python is informed about by the first line: # -*- coding: utf-8 -*-. This means that for example an ä is 2 bytes: 11000011 10100100 (hexval "c3a4"). There are two types of strings in Python 2.x: "" aka byte strings and u"" aka unicode string. For these two types two different things happen when parsing a file: If python encounters a non ascii char in a byte string (e.g., "ä") it will check if there's an input encoding given (yes, utf8) and then check if the 2 bytes ä is a valid utf-8 encoded char (yes it is). It will then simply keep the ä as its 2 byte utf-8 encoding in this byte-string internal representation. If you print it and you're lucky to have a utf8 console you'll see an ä again. If you're not lucky and for example have a iso-8859-15 encoding on your console you'll see 2 strange chars (probably Ã€) instead. So python will simply write the byte-string to output. >>> print "ä" #BAD! ä If there was no encoding given, we'd get a SyntaxError: Non-ASCII character 'xc3' in file ..., which is the first byte of our 2 byte ä. Where did the 'xc3' come from? Well, this is python's way of writing a non ascii byte to ascii output (which is always safe, so perfect for this error message): it will write a x and then two hex chars for each byte. Python does the same if we call: >>> print repr("ä") 'xc3xa4' Or just >>> "ä" 'xc3xa4' It also works the other way around, so you can give an arbitrary byte by using the same xXX escape sequences: >>> print "xc3xa4" #BAD! ä Oh look, we hit the utf8 representation of an ä, what a luck. You'll ask how do I then print "xc3xa4" to my console? You can either double all "" or tell python it's a raw string: >>> print "\xc3\xa4" xc3xa4 >>> print r"xc3xa4" xc3xa4 If python encounters a unicode string in our document (e.g., u"ä") it will use the specified file encoding to convert our 2 byte utf8 ä into a unicode string. This is the same as calling "ä".decode(myFileEncoding): >>> print u"ä" # BAD for another reason! ä >>> u"ä" u'xe4' >>> "ä".decode("utf-8") u'xe4' Python's internal unicode representation of this string is never exposed to the user (it could be UTF-16 or 32 or anything else, anyone?). The hex e4 corresponds to 11100100, the unicode ord value of the char ä, which is decimal 228. >>> ord(u'ä') 228 And the same again backwards, we can use the xXX escaping to denote a hex unicode point or raw not to interpret such escaping: >>> print u"xe4" ä >>> print ur"xe4" xe4 Oh, noticed the difference? This time print did some magic. I told you, you'll never see python's internal representation of a unicode string. So whenever print receives a unicode string it will try to convert it to your output encoding (sys.out.encoding), which works in a terminal, but won't work if you're for example redirecting output to a file. In such cases you have to convert the string into the desired encoding explicitly: >>> u"ä".encode("utf8") 'xc3xa4' >>> print u"ä".encode("utf8") #BAD! ä If that last line confused you a bit: We converted the unicode string to a byte-string, which was then simply copied byte-wise by print and voila, we got an ä. This all is done before the string even reaches doctest. So you might have written something like all the above in doctests, and probably saw them failing. In most cases you probably just forgot the ur'''prefix''', but sometimes you had it and were confused. Well this is good, as all of the above #BAD! examples don't make much sense. Bummer, right. The reason is: we made assumptions on the default encoding all over the place, which is not a thing you would ever want to do in production code. We did this by setting sys.setdefaultencoding("UTF-8") below. Without this you'll usually get unicode warnings like this one: "UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal". Just fire up a python interpreter (not pydev, as I noticed it seems to fiddle with the default setting). Try: u"ä" == "ä" You should get: __main__:1: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal False This actually is very good, as it warns you that you're comparing some byte-string from whatever location (could be a file) to a unicode string. Shall python guess the encoding? Silently? Probably a bad idea. Now if you do the following in your python interpreter: import sys reload(sys) sys.setdefaultencoding("utf8") u"ä" == "ä" You should get: True No wonder, you explicitly told python to interpret the "ä" as utf8 encoded when nothing else specified. So what's the problem in our docstrings again? We had these bad examples: >>> print "ä" #BAD! ä >>> print "xc3xa4" #BAD! ä >>> print u"ä".encode("utf8") #BAD! ä Well, we're in a ur'''docstring''' here, so what doctest does is: it takes the part after >>> and exec(utes) it. There's one special feature of exec i wasn't aware of: if you pass a unicode string to it, it will revert the char back to utf-8: >>> exec u'print repr("ä")' 'xc3xa4' >>> exec u'print repr("xe4")' 'xc3xa4' This means that even though one might think that print "ä" in this unicode docstring will get print "xe4", it will print as if you wrote print "ä" outside of a unicode string, so as if you wrote print "xc3xa4". Let this twist your mind for a second. The doctest will execute as if there had been no conversion to a unicode string, which is what you want. But now comes the comparison. It will see what comes out of that and compare to the next line from this docstring, which now is a unicode "ä", so xe4. Hence we're now comparing u'xe4' == 'xc3xa4'. If you didn't notice, this is the same we did in the python interpreter above: we were comparing u"ä" == "ä". And again python tells us "Hmm, don't know shall I guess how to convert "ä" to u"ä"? Probably not, so evaluate to False. Summary: Always specify the source encoding: # -*- coding: utf-8 -*- and _ALWAYS_, no excuse, use utf-8. Repeat it: I will never use iso-8859-x, latin-1 or anything else, I'll use UTF-8 so I can write Jörn and he can actually read his name once. Use ur'''...''' surrounded docstrings (so a raw unicode docstring). You can also use ru'''...''', but I always think Russian strings? Never compare a unicode string with a byte string. This means: don't use u"ä" and "ä" mixed, they're not the same. Also the result line can only match unicode strings plain ascii, no other encoding. The following are bad comparisons, as they will compare byte- and unicode strings. They'll cause warnings and eval to false: #>>> u"ä" == "ä" #False #>>> "ä".decode("utf8") == "ä" #False #>>> print "ä" #ä So finally a few working examples: >>> "ä" # if file encoding is utf8 'xc3xa4' >>> u"ä" u'xe4' Here both are unicode, so no problem, but nevertheless a bad idea to match output of print due to the print magic mentioned above and think about i18n: time formats, commas, dots, float precision, etc. >>> print u"ä" # unicode even after exec, no prob. ä Better: >>> "ä" == "ä" # compares byte-strings True >>> u"ä".encode("utf8") == "ä" # compares byte-strings True >>> u"ä" == u"ä" # compares unicode-strings True >>> "ä".decode("utf8") == u"ä" # compares unicode-strings True """ pass if __name__ == "__main__": import sys reload(sys) sys.setdefaultencoding("UTF-8") # DON'T DO THIS. READ THE ABOVE @UndefinedVariable import doctest doctest.testmod()