<s>[INST] Count occurrence of a character in a string What's the simplest way to count the number of occurrences of a character in a string?
e.g. count the number of times 'a' appears in 'Mary had a little lamb'
 [/INST] 
str.count(sub[, start[, end]])
Return the number of non-overlapping occurrences of substring sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.

>>> sentence = 'Mary had a little lamb'
>>> sentence.count('a')
4

Or:
from collections import Counter
sentence = 'Mary had a little lamb'
print(Counter(list(sentence))['a'])

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