条件、循环和其他语句

1. print、import
   • 使用逗号输出多个表达式

     >>> name="Gumby"
     >>> salutation="Mr."
     >>> greeting="Hello,"
     ##同时输出三个变量
     >>> print greeting + salutation + name
     Hello,Mr.Gumby # 普通输出，相邻两个变量之间有空格
     >>> print greeting, salutation, name
     Hello, Mr. Gumby # 逗号输出，相邻两个变量之间有空格
     >>> print "%s %s %s" % (greeting, salutation, name)
     Hello, Mr. Gumby # %格式化字符串输出，有无空格看""内如何定义
     ##解决空格问题
     >>> greeting="Hello"
     >>> print greeting , "," , salutation , name
     Hello , Mr. Gumby
     >>> print greeting + "," , salutation , name
     Hello, Mr. Gumby
     ##语句结尾处打逗号会去掉回车
     text.txt:
     print "Hello,",
     print "world"
     cmd:
     py text.txt
     Hello, world

   • 导入

     1. import somemodule
     2. from somemodule import somefunction
     3. from somemodule import somefunction, anotherfunction, yetanotherfunction
     4. from somemodule import *
     

     当导入的两个函数重名时，只导入模块，或者as设置别名

     ##
     module1.open()
     module2.open()
     
     ##
     from module1 import open as open1
     open1()
     from module2 import open as open2
     open2()

2. 赋值魔法
   • 序列解包：将多个值的序列解开，然后放到变量的序列中。

     >>>values = 1,2,3
     >>>values
     (1,2,3)
     >>>x, y, z = values
     >>>print x, y, z
     1 2 3
     ##交换变量
     >>>x, y = y, x
     >>>print x, y, z
     2 1 3
     ##当函数返回序列或映射时，序列解包很好用
     >>> dic = {'name':{'one':'One','two':'Two'},'pho':{1:1,2:2}}
     >>> key, values = dic.popitem()
     >>> key
     'pho'
     >>> values
     {1: 1, 2: 2}
     >>> key, values = dic.popitem()
     >>> key
     'name'
     >>> values
     {'two': 'Two', 'one': 'One'}

   • 链式赋值

     >>>x = y = somefunction()
     

     注：关于 Python 链式赋值的坑 赋值从左往右：x = somefunction() -> y = somefunction()
   • 增量赋值

     >>>x+=1 x-=1 x*=1 x/=1 #x为任意数据类型。

3. 语句块：缩排的乐趣

   • test..txt:
     x=[1,2,3]
     for i in x:
         print i
     print "end"
     cmd:
     py test.txt
     1
     2
     3
     end

4. 条件和条件语句
   • 比较运算符： ==   <   >   <=   >=   !=    is    is not   in   not in 
   • 断言：assert

     >>>if number<=10 and number >=1:
     >>>    print "great"
     >>>elif number>=11:
     >>>     print "wonderful"
     >>>else:
     >>>    print "bad"
     
     >>>number = 101
     >>>assert number >=100, 'The number is too big.'
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     AssertionError: The number is too big.

5. 循环
6. 列表推导式-轻量级循环
   • 1
7. 三人行
   • 1