# encoding=utf-8
def count_occurence(s,letter):
if not isinstance(s,str) or not isinstance(letter,str):
return 0
times =0
if letter not in s:
return 0
else:
for i in s:
if i == letter:
times+=1
return times
print(count_occurence("aaa","a"))
print(count_occurence("aaa","b"))
print(count_occurence("aaa",2))
輸出結果：
>>> print(count_occurence("aaa","a"))
3
>>> print(count_occurence("aaa","b"))
0
>>> print(count_occurence("aaa",2))
0