[python基础(四)]条件和条件语句

1.print和import1.1 print 略1.2 import(1)impore somemodule     (2)from somemodule import somefunction(3)from somemodule import somefunction,anotherfunction(4)from somemodule import*(5)import somemodule as somename    #为整个模块提供别名(6)from somemodule import somefunction as somename    #为某个模块的某个函数提供别名

2.赋值2.1 序列解包：将多个值的序列解开，然后放到变量的序列中。2.2 链式赋值：将同一个值赋给多个变量。2.3 增量赋值：eg：x+=1

3.语句块：条件为真时执行或执行多次的一组语句，由代码前放置空格缩进语句创建。

4.条件语句4.1 布尔变量 python中的假：False None 0 “” () [] {}4.2 if语句4.3 else语句4.4 elif语句4.5 嵌套代码块4.6 条件（1）比较运算符

(2)相等运算符 ==

(3)同一性运算符 is

(4)成员资格运算符 in

(5)字符串和序列比较

(6)布尔运算符

4.7 断言： assert 放入检查点，确保某个条件一定为真才能让程序正常工作

5. 循环

5.1 while循环

5.2 for循环

5.3 循环遍历字典元素

5.4 迭代工具

(1) 并行迭代：同时迭代两个序列

(2)按索引迭代

(3)翻转和排序迭代

5.5 跳出循环

(1) break

(2) continue

(3) while True/break

5.6 循环中的else子句

6.列表推导式-轻量级循环

7.pass,del,exec

本章相关代码：# -*- coding: utf-8 -*-

#1.print 与import#1.1 print 使用逗号输出print ‘Age:‘,42   #Age: 42name=‘xiaming‘age=‘42‘print name,age   #xiaming 42

#2.赋值语句#2.1.序列解包:将多个值的序列解开，然后放到变量的序列中x,y,z=1,2,3print x,y,z  #1 2 3x,y=y,x       #2 1 3print x,y,zv=1,2,3x,y,z=vprint x     #1

#2.2.链式赋值 将同一个值赋给多个变量的捷径x=y=4print x,y

#2.3.增量赋值x=2x+=1x*=2a=‘bo‘a+=‘x‘a*=2print x,a  #6,boxbox

#3:语句块：缩排

#4.条件与条件语句#4.1.布尔变量的作用

#4.2 if  elif else语句name=raw_input(‘what is your name?‘)if name.endswith(‘ming‘):    print ‘hello,ming‘elif name.endswith(‘hong‘):    print ‘hello,hong‘else:    print ‘hello‘

#4.3 嵌套语句num=raw_input(‘input a number‘)if num>10:    if num<20:        print ‘10<num<20‘    else:        print ‘num>=20‘else:    print ‘num<=10‘

#5.循环#5.1.while循环x=1while x<=10:  print x  x+=1

name=‘‘while not name:    name=raw_input(‘enter your name:‘)print ‘Hello,%s!‘%name   #Hello,ming!

#5.2.for 循环names=[‘ming‘,‘hong‘,‘qiang‘,‘qing‘]for n in names:    print n

print range(10)  #[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] rang(0,10)for num in range(1,10):    print num

#5.3.循环遍历字典元素d={‘x‘:1,‘y‘:2,‘z‘:3}for key in d:    print key,d[key]    #y 2 x 1 z 3

#5.4.一些迭代工具#5.4.1 并行迭代names=[‘ming‘,‘hong‘,‘qiang‘,‘qing‘]ages=[10,11,12,13]for i in range(len(names)):    print names[i],‘is‘,ages[i],‘years old‘  #ming is 10 years old...

print zip(names,ages) #[(‘ming‘, 10), (‘hong‘, 11), (‘qiang‘, 12), (‘qing‘, 13)] 将两个序列压缩，返回一个元组的列表for n,a in zip(names,ages):    print n, ‘is‘,a, ‘years old‘   #ming is 10 years old...

#5.4.2按索引迭代#5.4.3翻转和排序迭代

#5.5.跳出循环#5.5.1breakfrom math import sqrtfor n in range(99,0,-1):    print n    root=sqrt(n)    if root==int(root):        print "the biggst is %s"%n        break

#5.5.2 continue

#5.5.3 while True/breakwhile True:    word=raw_input(‘Please enter a word:‘)    if not word:break    print ‘The word was ‘+word

#5.6 循环体中的else子句from math import sqrtfor n in range(99,80,-1):    print n    root=sqrt(n)    if root==int(root):        print "the biggst is %s"%n        break    else:        print "didn‘t find it"

#6 列表推导式-轻量级循环：利用其它列表创建新列表print [x*x for x in range(10)]   #[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]print [x*x for x in range(10) if x%3==0]  #[0, 9, 36, 81]print [(x,y,z) for x in range(2) for y in range(2) for z in range(2)]#[(0, 0, 0), (0, 0, 1), (0, 1, 0), (0, 1, 1), (1, 0, 0), (1, 0, 1), (1, 1, 0), (1, 1, 1)]

#7 三个语句：pass,del,exec#7.1 pass :#7.2 del:删除不再使用的对象#7.3 exec:执行一系列Py语句 exel:计算Py表达式，并且返回结果值