[프로그래머스 Lv.1]신규 아이디 추천

https://programmers.co.kr/learn/courses/30/lessons/72410?language=python3 

코딩테스트 연습 - 신규 아이디 추천

def solution(new_id):
    #1, #2
    answer = ''
    for i in new_id:
        char=i.lower()
        if char >= 'a' and char <= 'z':
            answer += char
        elif char >= '0' and char <= '9':
            answer += char
        elif char == '-' or char == '_' or char == '.':
            answer += char
        else:
            continue
    
    #3
    while '..' in answer:
        answer=answer.replace('..','.')
        print(3)
    print(answer)
    #4
    if len(answer) != 0:
        if answer[0] == '.':
            answer=answer[1:]
    if len(answer) != 0:
        if answer[-1] == '.':
            answer=answer[:-1]

    #5
    if answer == '':
        answer = 'a'

    #6
    if len(answer) >= 16:
        answer=answer[:15]
        if answer[-1] == '.': answer=answer[:-1]
    #7
    while len(answer) <= 2:
        answer+=answer[-1]
    return answer

print(solution('b......@'))