python 条件判断

计算机之所以能够很多自动化的任务,因为它可以自己做条件判断:比如,输入用户年龄,根据年龄打印不同的内容,在Python程序中,用if语句实现:age = input('please input your age!')print age;if age >= 18:    print 'your age is', age    print 'adult'else:    print  'your age is', age    print 'man'C:\Python27\python.exe C:/Users/TLCB/PycharmProjects/untitled/a2.pyplease input your age!1010your age is 10manProcess finished with exit code 0age = raw_input('please input your age!')print age;if age >= 18:    print 'your age is', age    print 'adult'else:    print  'your age is', age    print 'man'C:\Python27\python.exe C:/Users/TLCB/PycharmProjects/untitled/a2.pyplease input your age!1010your age is 10adultProcess finished with exit code 0此时用raw_input就不行if语句执行有个特点，它是从上往下判断，如果在某个判断上是True，把该判断对应的语句执行后，就忽略掉剩下的elif和else，所以，请测试并解释为什么下面的程序打印的是teenager：age = 20if age >= 6:    print 'teenager'elif age >= 18:    print 'adult'else:    print 'kid'循环:Pytho的循环有两种,一种是for..in，因此把list或tuple中的每个元素迭代出来,看例子:names = ['Michael', 'Bob', 'Tracy']for name in names:    print nameC:\Python27\python.exe C:/Users/TLCB/PycharmProjects/untitled/t1.pyMichaelBobTracy所以for x in ... 循环就是把每个元素带入变量x,然后执行缩进快的语句:sum = 0for x in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]:    sum = sum + xprint sumC:\Python27\python.exe C:/Users/TLCB/PycharmProjects/untitled/t1.py55如果要计算1-100的整数之和,从1写到100有点困难,幸好Python提供了一个range()函数,可以生成一个整数序列,比如range(5)生成的序列是从0开始小于5的整数:a=range(5)print aprint a[0];print a[1];print a[2];print a[3];print a[4];C:\Python27\python.exe C:/Users/TLCB/PycharmProjects/untitled/t1.py[0, 1, 2, 3, 4]01234第二种循环是while循环,只要条件满足,就不断循环,条件不满足就退出循环。sum = 0n = 99while n > 0:    sum = sum + n    n = n - 2print sum再议raw_input:最后看一个有问题的条件判断,使用raw_input()读取用户的输入，这样可以自己输入，程序运行得更有意思：输入1982，结果却显示00后，这么简单的判断Python也能搞错？当然不是Python的问题，在Python的交互式命令行下打印birth看看：>>> birth'1982'>>> '1982' < 2000False>>> 1982 < 2000True原因找到了！原来raw_input()读取的内容永远以字符串的形式返回,把字符串和整数比较就得不到期待的结果.# -*- coding: UTF-8 -*-import timei=0;while 1 == 1:    i=i+1;    time.sleep(5);    print iC:\Python27\python.exe C:/Users/TLCB/PycharmProjects/untitled/t1.py1234