How do I count letters in a string?

Question

Say I have a UTF-8 str, for example

my_str = "नमस्ते"  # ['न', 'म', 'स', '्', 'त', 'े']

how do I find how many letters it contains? len(my_str) returns 6, which is how many Unicode code points it contains. It's actually 4 letters long.

And bonus question: some languages define digraphs as a single letter (for example "Dh" is the 6th letter of the modern Albanian alphabet), how can I handle that edge case?

Answer 1

You want to segment text. This is governed in Unicode by UAX #29.

4 letters long

That terminology is incorrect/too narrow, it should say "4 grapheme clusters long".

Use the uniseg library:

from uniseg.graphemecluster import grapheme_clusters
for text in ('नमस्ते', 'Bo\u0304ris', 'Ꙝ̛͖͋҉ᄀᄀᄀ각ᆨᆨ'):
    print(list(grapheme_clusters(text)))
#['न', 'म', 'स्', 'ते']
#['B', 'ō', 'r', 'i', 's']
#['Ꙝ̛͋', 'ᄀᄀᄀ각ᆨᆨ']

# treat digraph 'dh' as a customised grapheme cluster
def albanian_digraph_dh(s, breakables):
    for i, breakable in enumerate(breakables):
        if s.endswith('d', 0, i) and s.startswith('h', i):
            yield 0
        else:
            yield breakable

# you can do all the digraphs like this
ALBANIAN_DIGRAPHS = {"Dh", "Gj", "Ll", "Nj", "Rr", "Sh", "Th", "Xh", "Zh"}
ALBANIAN_DIGRAPHS |= {digraph.lower() for digraph in ALBANIAN_DIGRAPHS}
def albanian_digraphs(s, breakables):
    for i, breakable in enumerate(breakables):
        yield 0 if s[i-1:i+1] in ALBANIAN_DIGRAPHS else breakable

# from https://sq.wiktionary.org/wiki/Speciale:PrefixIndex?prefix=dh
for text in ('dhallanik', 'dhelpëror', 'dhembshurisht', 'dhevështrues', 'dhimbshëm', 'dhjamosje', 'dhjetëballësh', 'dhjetëminutësh', 'dhogaç', 'dhogiç', 'dhomë-muze', 'dhuratë', 'dhëmbinxhi', 'dhëmbçoj', 'dhëmbëkatarosh'):
    print(list(grapheme_clusters(text, albanian_digraphs)))

#['dh', 'a', 'll', 'a', 'n', 'i', 'k']
#['dh', 'e', 'l', 'p', 'ë', 'r', 'o', 'r']
#['dh', 'e', 'm', 'b', 'sh', 'u', 'r', 'i', 'sh', 't']
#['dh', 'e', 'v', 'ë', 'sh', 't', 'r', 'u', 'e', 's']
#['dh', 'i', 'm', 'b', 'sh', 'ë', 'm']
#['dh', 'j', 'a', 'm', 'o', 's', 'j', 'e']
#['dh', 'j', 'e', 't', 'ë', 'b', 'a', 'll', 'ë', 'sh']
#['dh', 'j', 'e', 't', 'ë', 'm', 'i', 'n', 'u', 't', 'ë', 'sh']
#['dh', 'o', 'g', 'a', 'ç']
#['dh', 'o', 'g', 'i', 'ç']
#['dh', 'o', 'm', 'ë', '-', 'm', 'u', 'z', 'e']
#['dh', 'u', 'r', 'a', 't', 'ë']
#['dh', 'ë', 'm', 'b', 'i', 'n', 'xh', 'i']
#['dh', 'ë', 'm', 'b', 'ç', 'o', 'j']
#['dh', 'ë', 'm', 'b', 'ë', 'k', 'a', 't', 'a', 'r', 'o', 'sh']

You can install it with

pip install uniseg