Python学习笔记-基础语法

第七章 用户输入和while循环

• 一、input()函数
• 二、while循环
• 三、使用while循环来处理列表和字典

一、input()函数

1、int()函数：

• input()函数输出为字符串，使用int()将之转换为数值

age = input("请输入你的年龄：")
print(age >= 19)

输出结果为：
请输入你的年龄：11
Traceback (most recent call last):
 File "D:\Python_Work\Python学习\Python编程-从入门到实践\练习.py", line 2, in 
  print(age >= 19)
TypeError: '>=' not supported between instances of 'str' and 'int'

2、求模求商

>>> 10 // 2
5
>>> 10 % 2
0

二、while循环

prompt = "\nTell me something, and I will repeat it back to you: "
prompt += "\nEnter 'quit' to end the program. " + "\n"
message = ''
while message != 'quit':
 message = input(prompt)
 if message != 'quit':
  print(message)

输出结果为：

Tell me something, and I will repeat it back to you:
Enter 'quit' to end the program.
你好帅啊
你好帅啊

Tell me something, and I will repeat it back to you:
Enter 'quit' to end the program.
quit

1、使用标志高效运行while循环

prompt = "\nTell me something, and I will repeat it back to you: "
prompt += "\nEnter 'quit' to end the program. " + "\n"
active = True #标志
while active:
 message = input(prompt)
 if message == 'quit':
  active = False
 else:
  print(message)

输出结果：
Tell me something, and I will repeat it back to you:
Enter 'quit' to end the program.
你好帅啊
你好帅啊

Tell me something, and I will repeat it back to you:
Enter 'quit' to end the program.
quit

2、使用break退出循环

prompt = "\nTell me something, and I will repeat it back to you: "
prompt += "\nEnter 'quit' to end the program. " + "\n"
while True:
 city = input(prompt)
 if city == 'quit':
  break

输出结果为：
Tell me something, and I will repeat it back to you:
Enter 'quit' to end the program.
你好帅啊

Tell me something, and I will repeat it back to you:
Enter 'quit' to end the program.
quit

• 在任何Python循环中都可以使用break语句
• 可使用break语句来退出遍历列表或字典的for循环

3、在循环中使用continue

• continue：回到循环开头，根据条件测试结果决定是否继续执行循环
• 它不像break语句那样不再执行余下的代码并推出整个循环

current_number = 0
while current_number < 10:
 current_number += 1
 if current_number %2 == 0:
  continue #如果符合条件测试，continue让他回到while重新执行，直到不符合条件测试，打印current_number
print(current_number)

输出结果为：
1
3
5
7
9

三、使用while循环来处理列表和字典

• for循环中不应修改列表，否则将导致Python难以跟踪其中的元素
• 要在遍历列表的同时对其进行修改，可使用while循环

1、在列表之间移动元素

unconfirmed_users = ['alice','brian','candace']
confirmed_users = []
while unconfirmed_users: #列表空则为False
 current_user = unconfirmed_users.pop()
 print("Verifying user: " + current_user.title())
 confirmed_users.append(current_user)
print("\nThe following users have been confirmed: ")
for confirmed_user in confirmed_users:
  print(confirmed_user)

输出结果为：
Verifying user: Candace
Verifying user: Brian
Verifying user: Alice

The following users have been confirmed:
candace
brian
alice

2、删除包含特定值得所有列表元素

pets = ['dog','cat','dog','goldfish','cat','rabbit','cat']
print(pets)
while 'cat' in pets:
 pets.remove('cat')
print(pets)

输出结果为：
['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
['dog', 'dog', 'goldfish', 'rabbit']

3、使用用户输入来填充字典

responses = {}
polling_active = True
while polling_active:
 name = input("\nWhat is your name?\n ")
 response = input("Which mountain would you like to climb someday? \n")
 responses[name] = response
 repeat = input("Would you like to let another person respond? (yes/no) \n")
 if repeat == 'no':
  polling_active = False
print("\n--- Poll Results ---")
for name, response in responses.items():
 print("\n" + name.title() + " would like to climb " + response + ".\n")
输出结果为：
What is your name?
小明
Which mountain would you like to climb someday?
黄山
Would you like to let another person respond? (yes/no)
yes

What is your name?
小刚
Which mountain would you like to climb someday?
泰山
Would you like to let another person respond? (yes/no)
no

--- Poll Results ---
小明 would like to climb 黄山.

小刚 would like to climb 泰山.