Count occurrence of a character in a Python string

Question

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'

Answer 1

Regular expressions maybe?

import re
my_string = "Mary had a little lamb"
len(re.findall("a", my_string))

Answer 2

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.

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

Answer 3

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

Answer 4

myString.count('a');

more info here

Answer 5

"aabc".count("a")