返回字符串中最长数字子串

'''
一个字符串 1dsl2323j2454665757 ，返回最长数字子串
返回：2454665757
'''

def num(a_str):
    max_number_temp,temp=[],[]
    i,j=0,len(a_str)

    while i<j:
        if a_str[i].isdigit():
            temp.append(a_str[i])

        else:
            if len(temp)>len(max_number_temp):
                max_number_temp=temp
            temp = []

        i += 1

    if len(temp) > len(max_number_temp):
        max_number_temp = temp

    return "".join(max_number_temp)

if __name__=="__main__":
    a_str="1dsl2323j2454665757"
    print(num(a_str))