使用递归获取python中的子字符串

Question

how can I use recursion to find the amount of 'a' that is in a string:

example: get_a('halloa') -> 2

here is what I have:

    def get_a(string):
        '''
        return how many times a exist in the string using recursion
        '''
        if string == '':
            return 0
        if string[0] == 'a':
            return 1
    return get_a(string[1:])

Answer 1

the problem in your code is that you stop the recursion when you find the first a . You'll want to call get_a and collect the a s you've already found:

def get_a(string):
    '''
    return how many times a exist in the string using recursion
    '''
    if string == '':
        return 0
    if string[0] == 'a':
        return 1 + get_a(string[1:])
    return get_a(string[1:])