问题
Example in Python:
>>> s = 'ı̇'
>>> len(s)
2
>>> list(s)
['ı', '̇']
>>> print(", ".join(map(unicodedata.name, s)))
LATIN SMALL LETTER DOTLESS I, COMBINING DOT ABOVE
>>> normalized = unicodedata.normalize('NFC', s)
>>> print(", ".join(map(unicodedata.name, normalized)))
LATIN SMALL LETTER DOTLESS I, COMBINING DOT ABOVE
As you can see, NFC normalization does not compose the dotless i + a dot to a normal i. Is there a rationale for this? Is this an oversight? Or is it not included because NFC is supposed to be the perfect inverse of NFD (and one wouldn’t want to decompose i to dotless i + dot).
回答1:
While NFC isn't the "perfect inverse" of NFD, this follows from NFC being defined in terms of the same decomposition mappings as NFD. NFC is basically defined as NFD followed by recomposing certain NFD decomposition pairs. Since there's no decomposition mapping for LATIN SMALL LETTER I, it can never be the result of a recomposition.
来源：https://stackoverflow.com/questions/50086824/why-do-latin-small-letter-dotless-i-combining-dot-above-not-get-normalized-to