学习笔记4(第5章:if语句)
1、在Python中检查是否相等时是区分大小写的。
2、检查多个条件可以使用关键字and、or。 检查特定值是否包含在列表中,可使用关键字in。 检查特定值是否不包含在列表中,可以使用关键字 not in。
3、布尔表达式的结果要么是True,要么是False。
4、用for循环运行前检查列表是否为空。
requested_toppings = [] if requested_toppings: for requested_topping in requested_toppings: print("Adding " + requested_topping + ".") print("\nFinished making your pizza!") else: print("Are you sure you want a plain pizza?")
这个列表为空,因此输出结果为:
Are you sure you want a plain pizza?
5、p79 5-10 检查用户名,确保每一个用户名的独一无二性。(确保比较时不区分大小写,如果'John’已被使用,应拒绝用户名‘JOHN’)
current_users = ['andy','AMY','Luu','jier','juzi'] new_users = ['Amy','luyan','xiao','luu','pong'] current_users_lower = [user.lower() for user in current_users] #也可以使用下面的方法
# current_users_lower = [] # for user in current_users: # current_users_lower.append(user.lower()) for new_user in new_users: if new_user.lower() in current_users_lower: print("Sorry " + new_user + ", that name is taken.") else: print("Great, " + new_user + " is still available.")
运行结果:
Sorry Amy, that name is taken. Great, luyan is still available. Great, xiao is still available. Sorry luu, that name is taken. Great, pong is still available.