Count the number of occurrences 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 that 'a' appears in 'Mary had a little lamb'.

Solution 1:

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

Solution 2:

You can use count() :

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

Solution 3:

As other answers said, using the string method count() is probably the simplest, but if you're doing this frequently, check out collections.Counter:

from collections import Counter
my_str = "Mary had a little lamb"
counter = Counter(my_str)
print counter['a']