Count the number occurrences of a character in a string
What's the simplest way to count the number of occurrences of a character in a string?
eg count the number of times 'a' appears in 'Mary had a little lamb'
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
你可以使用count（）：
>>> 'Mary had a little lamb'.count('a')
4
正如其他答案所说，使用字符串方法count（）可能是最简单的，但如果您经常这样做，请检查集合.Counter：
from collections import Counter
str = "Mary had a little lamb"
counter = Counter(str)
print counter['a']
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