python - problems with regular expression and unicode

Question

Hi I have a problem in python. I try to explain my problem with an example.

I have this string:

>>> string = 'ÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿÀÁÂÃ'
>>> print string
ÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿÀÁÂÃ

and i want, for example, replace charachters different from Ñ,Ã,ï with ""

i have tried:

>>> rePat = re.compile('[^ÑÃï]',re.UNICODE)
>>> print rePat.sub("",string)
�Ñ�����������������������������ï�������������������Ã

I obtained this �. I think that it's happen because this type of characters in python are represented by two position in the vector: for example \xc3\x91 = Ñ. For this, when i make the regolar expression, all the \xc3 are not substitued. How I can do this type of sub?????

Thanks Franco

Answer 1

You need to make sure that your strings are unicode strings, not plain strings (plain strings are like byte arrays).

Example:

>>> string = 'ÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿÀÁÂÃ'
>>> type(string)
<type 'str'>

# do this instead:
# (note the u in front of the ', this marks the character sequence as a unicode literal)
>>> string = u'\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\xc0\xc1\xc2\xc3'
# or:
>>> string = 'ÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿÀÁÂÃ'.decode('utf-8')
# ... but be aware that the latter will only work if the terminal (or source file) has utf-8 encoding
# ... it is a best practice to use the \xNN form in unicode literals, as in the first example

>>> type(string)
<type 'unicode'>
>>> print string
ÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿÀÁÂÃ

>>> rePat = re.compile(u'[^\xc3\x91\xc3\x83\xc3\xaf]',re.UNICODE)
>>> print rePat.sub("", string)
Ã

---

When reading from a file, string = open('filename.txt').read() reads a byte sequence.

To get the unicode content, do: string = unicode(open('filename.txt').read(), 'encoding'). Or: string = open('filename.txt').read().decode('encoding').

The codecs module can decode unicode streams (such as files) on-the-fly.

Do a google search for python unicode. Python unicode handling can be a bit hard to grasp at first, it pays to read up on it.

I live by this rule: "Software should only work with Unicode strings internally, converting to a particular encoding on output." (from http://www.amk.ca/python/howto/unicode)

I also recommend: http://www.joelonsoftware.com/articles/Unicode.html