题目: 输入一个用户名,检查是否有效。 有效标准: 长度在6~12; 只能包含小写字母、数字、下划线。 视频教程: Python入门100题之011:检查用户名 代码1: line = input("输入用户名:") def is_valid(name: str): for c in name: if c.islower() or c.isnumeric() or c == "_": continue return False if 6 <= len(name) <= 12: return True return False print(is_valid(line)) 代码2: line = input("输入用户名:") def is_valid(name: str): flags = [] for c in name: if c.islower() or c.isnumeric() or c == "_": flags.append(1) else: flags.append(0) if not all(flags): return False if 6 <= len(name) <= 12: return True return False print(is_valid(line)) 代码3: line = input("输入用户名:") def is_valid(name: str): flags = [] for c in name: if c.islower() or c.isnumeric() or c == "_": flags.append(1) else: flags.append(0) if sum(flags) != len(name): return False if 6 <= len(name) <= 12: return True return False print(is_valid(line))