Unicode y encodings
De WikiEducator
Contenido
Conocimiento previo
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Una cadena Unicode es una secuencia de code points, que son números de 0 a 0x10ffff. Esta secuencia se tiene que representar en un conjunto de bytes (valores de 0 a 255) en memoria. Las reglas para traducir una cadena Unicode a una secuencia de bytes se llama encoding.
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El problema
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¿Qué significa esto? UnicodeDecodeError: 'ascii' codec can't decode byte 0xc4 in position 10: ordinal not in range(128) >>> f = open('aragon.txt') >>> aragon_utf8 = f.read() >>> aragon_utf8 'Arag\xc3\xb3n' >>> len(aragon_utf8) 7 >>>type(aragon_utf8) <type 'str'> >>> unicode(aragon_utf8) UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 4: ordinal not in range(128) # el problema: >>> sys.getdefaultencoding() 'ascii' >>> aragon_uni = aragon_utf8.decode('utf-8') >>> aragon_uni u'Arag\xf3n' >>> len(aragon_uni) 6 |
Conversión y codificación
s.decode(encoding) # <type 'str'> to <type 'unicode'> >>> 'caña'.decode() Traceback (most recent call last): File "<stdin>", line 1, in <module> UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in range(128) >>> 'caña'.decode(errors='ignore') u'caa' >>> 'caña'.decode(errors='replace') u'ca\ufffd\ufffda' >>> 'caña'.decode('utf-8') u'ca\xf1a' u.encode(encoding) # <type 'unicode'> to <type 'str'> >>> u'caña'.encode('ascii', 'ignore') 'caa' >>> u'caña'.encode('ascii', 'replace') 'ca?a' >>> u'caña'.encode('ascii') Traceback (most recent call last): File "<stdin>", line 1, in <module> UnicodeEncodeError: 'ascii' codec can't encode character u'\xf1' in position 2: ordinal not in range(128) >>> u'caña'.encode('utf-8') 'ca\xc3\xb1a' |
Normalizar cadena
import unicodedata def textoplano(s): def normalize(c): return unicodedata.normalize("NFD", c)[0] # NFD: Normal Form Decomposition return ''.join(normalize(c) for c in s) >>> textoplano('una cigüeña hábil') "una ciguena habil" |
Ficheros con codecs
import codecs # open(filename, mode='rb', encoding=None, errors='strict', buffering=1) f = codecs.open('archivo', encoding='utf-8') for linea in f: print linea import codecs >>> enc, dec, read_wrap, write_wrap = codecs.lookup('utf-8') >>> f = open('utf8test.xml', 'wb') >>> f = write_wrap(f) >>> dec('caña') (u'ca\xf1a', 5) >>> enc(u'caña') ('ca\xc3\xb1a', 4) |
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