신규 아이디 추천 (2021 KAKAO BLIND RECRUITMENT)

def solution(new_id):
    allow = list('abcdefghijklmnopqrstuvwxyz-_.1234567890')
    new_id = new_id.lower()
    print(new_id)
    step_2= []
    for c in new_id:
        if c in allow: 
            step_2.append(c)
    new_id = ''.join(step_2)
    print(new_id)
    
    step_3 = []
    continue_flag = False
    for c in new_id:
        if c != '.':
            step_3.append(c)
            continue_flag = False
        if c == '.':
            if continue_flag == False:
                step_3.append(c)
                continue_flag = True
 
    new_id = ''.join(step_3)
    print(new_id)
    
    while len(new_id) >=1 and new_id[0] == '.': 
        if len(new_id) == 1: 
            new_id = ''
            break
        else:new_id = new_id[1:]
        
    while len(new_id) >=1  and new_id[-1] == '.' :
        if len(new_id) == 1: 
            new_id = ''
            break
        new_id = new_id[:-1]
    
    if len(new_id) == 0 : new_id = 'a'
    if len(new_id) >=16:
        new_id = new_id[:15]
        if new_id[-1] == '.' :new_id = new_id[:-1]
    
    while len(new_id) <=2:
        new_id = new_id + new_id[-1]
    print(new_id)
    return new_id