Notes on Python cookbook 3rd (2.9): standardizing Unicode text

Giant ship 2020-11-13 01:52:35
notes python cookbook 3rd rd


take Unicode Text Standardization

problem

You're dealing with Unicode character string , You need to make sure that all strings have the same representation at the bottom .

solution

stay Unicode in , Some characters can be represented by more than one legal encoding . To illustrate , Consider the following example :

>>> s1 = 'Spicy Jalape\u00f1o'
>>> s2 = 'Spicy Jalapen\u0303o'
>>> s1
'Spicy Jalapeño'
>>> s2
'Spicy Jalapeño'
>>> s1 == s2
False
>>> len(s1)
14
>>> len(s2)
15
>>>

The text here ”Spicy Jalapeño” Two forms are used to express . The first is to use whole characters ”ñ”(U+00F1), The second one uses Latin letters ”n” Followed by a ”˜” The combined characters of (U+0303).

Using multiple representations of characters in programs that need to compare strings can cause problems . To fix this problem , You can use unicodedata The module standardizes the text first :

>>> import unicodedata
>>> t1 = unicodedata.normalize('NFC', s1)
>>> t2 = unicodedata.normalize('NFC', s2)
>>> t1 == t2
True
>>> print(ascii(t1))
'Spicy Jalape\xf1o'
>>> t3 = unicodedata.normalize('NFD', s1)
>>> t4 = unicodedata.normalize('NFD', s2)
>>> t3 == t4
True
>>> print(ascii(t3))
'Spicy Jalapen\u0303o'
>>>

normalize() The first parameter specifies how strings are normalized . NFC Indicates that the character should be a whole group become ( For example, use a single encoding if possible ), and NFD The representation character should be decomposed into several combined characters to represent .

Python It also supports standardized forms of extensions NFKC and NFKD, When they deal with certain characters Added additional compatibility features . such as :

>>> s = '\ufb01' # A single character
>>> s
' fi'
>>> unicodedata.normalize('NFD', s)
' fi'
# Notice how the combined letters are broken apart here
>>> unicodedata.normalize('NFKD', s)
'fi'
>>> unicodedata.normalize('NFKC', s)
'fi'
>>>

Discuss

Standardization for anything that needs to be dealt with in a consistent way Unicode The program of text is very important . This is especially true when dealing with strings from user input and it's hard for you to control the encoding .

Standardization of characters is also important when cleaning and filtering text . such as , Suppose you want to erase some of the diacritical notes from the text ( Maybe it's for searching and matching ):

>>> t1 = unicodedata.normalize('NFD', s1)
>>> ''.join(c for c in t1 if not unicodedata.combining(c))
'Spicy Jalapeno'
>>>

The last example shows unicodedata Another important aspect of the module , That is to test the tool function of character class . combining() Function can test whether a character is a harmony character . There are other functions in this module for finding character categories , Test for numeric characters, etc .

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