Python变量
变量为存储在内存中值，意味着在创建变量时会在内存中开辟一个空间，基于变量的数据类型，解释器会分配指定内存，并决定什么数据可以被存储在内存中。因此，变量可以指定不不同的数据类型，这些变量可以存储整数，小数或字符。
格式：变量名 = 值
命名规则：
1.数字、字母、下划线（_）组成
2.不能以数字开头
3.不能用Python关键字
特别注意：
不要汉字当变量
全局变量为全大写（CHINA = 1949）
变量、函数用下划线。类似驼峰体。
1 ['and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'exec', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'not', 'or', 'pass', 'print', 'raise', 'return', 'try', 'while', 'with', 'yield']
1 [root@hyz ~]# python 2 Python 2.7.5 (default, Aug 4 2017, 00:39:18) 3 [GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux2 4 Type "help", "copyright", "credits" or "license" for more information. 5 >>> counter = 100 # 赋值整型变量 6 >>> area = 89.7 # 浮点型 7 >>> name = 'Peter' # 字符串 8 >>> print(counter) 9 100 10 >>> print(area) 11 89.7 12 >>> print(name) 13 Peter
多个变量赋值
Python允许同时为多个变量 赋值
1 >>> a = b = c = 1 2 >>> print(a) 3 1 4 >>> print(c) 5 1 6 >>>
创建一个整型对象，值为1 ，三个变量被分配到相同的内存空间上。
多个对象指定多个变量
1 >>> a,b,c, = 0,2,'Peter' 2 >>> print(a,b,c) 3 (0, 2, 'Peter')
if语句
基本格式
1 if 条件: 2 pass 3 elif 条件: 4 pass 5 else: 6 pass 7 8 #!/usr/bin/python 9 # -*- coding:utf-8 -*- 10 number = 9 11 numbers = int(input('输入数字:')) 12 if numbers == number: 13 print('yes') 14 elif numbers < number: 15 print('small') 16 else: 17 print('big') 18 19 执行结果： 20 [root@hyz python3]# 21 [root@hyz python3]# python 1.py 22 输入数字:1 23 small 24 [root@hyz python3]# python 1.py 25 输入数字:9 26 yes 27 [root@hyz python3]# python 1.py 28 输入数字:10 29 big 30 [root@hyz python3]#
if语句自上而下匹配条件，最多匹配一次，可以匹配不上
whlie循环
基本格式
1 while 条件: 2 pass 3 4 #!/usr/bin/python 5 # -*- coding:utf-8 -*- 6 while True: 7 print('Peter is good') #死循环
while True 死循环。
1.条件不给True
2.满足某种条件内部破坏循环
for 循环
基本格式
1 for i in 可迭代对象: 2 print(i) 3 4 #!/usr/bin/python 5 # -*- coding:utf-8 -*- 6 for i in [1,2,3,4,5,6]: 7 print(i)
continue 和break
continue # 跳出当前这一次循环
break # 跳出当前循环
1 #!/usr/bin/python 2 # -*- coding:utf-8 -*- 3 for i in [1,2,3,4,5,6]: 4 if i == 1: 5 continue 6 if i == 6: 7 break 8 print(i)
此参数制度循环语句（while和for生效），遇到好几个语句、循环嵌套的情况，当运行结果与预期不符时，用print打印排查
基本练习：
求1-100的所有数的和
1 count = 1 2 sum = 0 3 while count < 101: 4 sum += count 5 count += 1 6 print(sum) 7 8 9 sum = 0 10 for i in range(1,101): 11 sum += i 12 print(sum)
输出1-100内的所有奇数
1 for i in range(1,101): 2 if i %2 == 0: 3 continue 4 print(i) 5 6 7 count = 1 8 while count < 101: 9 if count % 2 == 1: 10 print(count) 11 count += 1
输出1-100内的所有偶数
1 for i in range(1,101): 2 if i %2 == 1: 3 continue 4 print(i) 5 6 count = 1 7 while count < 101: 8 if count % 2 == 0: 9 print(count) 10 count += 1
求1-2+3-4+5......99的所有数的和
1 sum = 0 2 for i in range(1, 100): 3 if i % 2 == 0: 4 sum -= i 5 else: 6 sum += i 7 print(sum) 8 9 count = 1 10 sum = 0 11 while count < 100: 12 if count % 2 == 0: 13 sum -= count 14 else: 15 sum += count 16 count += 1 17 print(sum)
用户登录（三次机会）
1 import time 2 count = 0 3 account = 'Peter' 4 password = 'xqd521' 5 while count < 3: 6 user_account = input('Please enter the account:') 7 user_password = input('Please enter your password:') 8 if user_account == account: 9 print('Welcome!') 10 break 11 else: 12 print('Account password does not match, please re-enter') 13 count += 1 14 if count == 3: 15 print('There are too many input errors. Please reenter after 15 seconds!') 16 time.sleep(15) 17 18 19 20 21 22 # !/usr/bin/python 23 # -*- coding:utf-8 -*- 24 25 import time 26 user_list = [ 27 {'username':'root','password':'123'}, 28 {'username':'administrator','password':'123'}, 29 {'username':'god','password':'123'} 30 ] 31 count = 1 32 while True: 33 user_name = input('UserName:') 34 user_password = input('Password:') 35 flag = False 36 user_info = {'username':user_name,'password':user_password} 37 if user_info in user_list: 38 print('Welcome!') 39 break 40 else: 41 print('Account password does not match, please re-enter!') 42 count += 1 43 if count == 4: 44 print('There are too many input errors. Please reenter after 15 seconds!') 45 time.sleep(15) 46 break