How Can Python\'s `unicodedata` Module Normalize Unicode Strings for Consistent Manipulation?

Normalizing Unicode

Python's unicodedata module provides methods for manipulating Unicode strings. One common task is to normalize a string so that it uses the simplest possible representation, eliminating duplicate Unicode entities.

Problem

Consider the following example:

import unicodedata

char = "á"
len(char)
[unicodedata.name(c) for c in char]

The result shows that the string "á" is normalized to its simplest form: "LATIN SMALL LETTER A WITH ACUTE". However, if we reverse the order of the characters:

char = "á"
len(char)
[unicodedata.name(c) for c in char]

The result is decomposed into two separate characters: "LATIN SMALL LETTER A" and "COMBINING ACUTE ACCENT". This behavior is inconsistent and can complicate string manipulation.

Solution

To normalize a Unicode string consistently, use the .normalize() function from the unicodedata module. The NFC form (Normal Form Composed) returns composed characters, while the NFD form (Normal Form Decomposed) gives you decomposed, combined characters.

For example, using the same Unicode combination from above:

print(ascii(unicodedata.normalize('NFC', '\u0061\u0301')))
print(ascii(unicodedata.normalize('NFD', '\u00e1')))

The output shows that the NFC form produces the composed character "é", while the NFD form produces the decomposed sequence "au0301".

Additional forms, NFKC and NFKD, deal with compatibility codepoints. These forms replace compatibility characters with their canonical form. For instance:

unicodedata.normalize('NFKC', '\u2167')

Transforms the Roman numeral eight codepoint (U 2167) into the ASCII sequence "VIII".

Note that not all transformations are commutative. Decomposing a composed character and then recompounding it may not result in the original sequence. The Unicode standard maintains a list of exceptions for this behavior.

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