基本语句

#######################################
###############基本语句################
#######################################

赋值
>>> nudge=1
>>> wink=2
>>> A,B=nudge,wink	# 元组
>>> A,B
(1, 2)
>>> [C,D]=[nudge,wink]	# 列表
>>> C,D
(1, 2)
>>> nudge,wink = wink, nudge	# 元组：交换值
>>> nudge,wink			
(2, 1)


表达式
print语句
>>> print 'hello world'
hello world
>>> 'hello world'
'hello world'
>>> import sys
>>> sys.stdout.write('hello world\n')
hello world


if语句

>>> if 1:
...     print 'true'
...
...
true
>>> if not 1:
...     print 'true'
... else:
...     print 'false'
...
false
>>>


>>> choice='ham'
>>> print{'spam':1.25,		# 一个基于字典的'switch'
...       'ham':1.99,		# 默认用has_key（）条件
...       'eggs': 0.99,
...       'bacon': 1.10}[choice]


>>> x='killer rabbit'
>>> if x=='oger':		# 复合语句 首行以":"缩进语句
...     print "how's jessica?"	# 一个或多个首行缩进的嵌套语句，这些缩进的语句称之为块（block）或套（suite）
... elif x=='bugs':
...     print "what's up doc?"
... else:
...     print 'run away!run away!'
...
run away!run away!


----语句的界定----
>>> if (a==b and	# 一句语句两行 可以用括号）
... c==d):
...     print 'haha'
...
haha


>>> a=1
>>> b=1
>>> c=2
>>> d=2
>>> if a==b \	# 一句语句两行 可以用\
... and c==d:
...     print 'ok'
...
ok


>>> x=1;y=2;print x   #不是一句简单句


>>> 2<3,3<2
(True, False)
>>> 2 or 3
2
>>> 2 or 3, 4 or 5	# 如果真则返回左边的操作符
(2, 4)
>>> [] or 3
3
>>> [] or []
[]


while循环

一般格式
while <条件>:		# 循环测试
	<语句1>		# 循环体
else:			# 可选的else
	<语句2>		# 如果不是因为break而退出循环运行

>>> while 1:
...     print 'Type Ctrl-C to stop me!'

Type Ctrl-C to stop me!
Type Ctrl-C to stop me!
Type Ctrl-C to stop me!
Type Ctrl-C to stop me!
Type Ctrl-C to stop me!
Type Ctrl-C to stop me!
Type Ctrl-C to stop me!^C

>>> x= 'spam'
>>> while x:
...     print x
...     x=x[1:]	# 从x中取出第一个字符
...
spam
pam
am
m

>>> a=0;b=10
>>> while a < b:
...     print a,
...     a=a+1
...
0 1 2 3 4 5 6 7 8 9


----break continue pass else循环----
break 跳出最近的包围它的循环（通过整个循环语句）
continue 跳至最近的包围它的循环顶部（到循环的首行）
pass 什么都不做：只是一个占位的空语句。
else循环 运行并且只有在循环正常退出的情况下运行。

一般循环格式

while<条件测试>:
	<语句>
	if<条件测试>:break	#现在跳出循环，忽略else
	if<条件测试>:continue	#现在转到循环顶部
else：
	<语句>			#如果我们没遇上break

>>> x=10
>>> while x>0 :
...     x=x-1
...     if x%2 != 0: continue
...     print x,
...
8 6 4 2 0

>>> x=10
>>> a=1
>>> tmp=1
>>> while x>0:	#阶乘
...     a=a*tmp
...     tmp=tmp+1
...     x=x-1
...
>>> a
3628800



whwu@master:~/script/python/example> cat charpter3_exam1.py
#!/usr/bin/env python
# Fibonacci series up to n

a = int(input('number:'))   #a的数字类型是 整形 如果变成float 则会有小数

x=a/2

while x>1:
        if a%x == 0:
                print a,'has factor',x
                break
        x=x-1
else:
        print a,'is prime'
whwu@master:~/script/python/example> ./charpter3_exam1.py
number:39
39 has factor 13
whwu@master:~/script/python/example> ./charpter3_exam1.py
number:37
37 is prime


----for循环----

for<目标> in <对象>:	# 该目标赋以对象的项
	<语句>		# 重复循环体：使用目标
else:
	<语句>		# 如果我们没遇上break

>>> for x in ["spam","eggs","ham"]:
...     print x,
...
spam eggs ham

>>> sum=0
>>> for x in [1,2,3,4]:
...     sum=sum+x
...
>>> sum
10


>>> prod=1
>>> for item in [1,2,3,4]:
...     prod=prod*item
...
>>> prod
24


for循环也适用于字符串和元组
>>> for x in S:
...     sys.stdout.write('%s' %x)
...
lumberjack


>>> for i in range(6):
...     for j in range(i):
...             print '*',
...     print
...

*
* *
* * *
* * * *
* * * * *
>>> import sys
>>> for i in range(6):
...     for j in range(i):
...             sys.stdout.write('*')  #标准输出
...     print
...

*
**
***
****
*****


>>> items=["aaa",111,(4,5),2.01]
>>> tests=[(4,5),3.14]
>>> for key in tests:				# 所有的键
...     for item in items:			# 所有的项
...             if item == key:			# 检查是否匹配
...                     print key,"was found"
...                     break
...     else:					# 嵌套的else循环是重要的，它与内部for循环首行的缩进处于同一列，所以它
...             print key,"not found!"		# 它是与内部循环关联的（而不是if或外部的for）
...
(4, 5) was found
3.14 not found!

--in的操作--
>>> for key in tests:
...     if key in items:
...             print key,"was found"
...     else:
...             print key,"not found!"
...
(4, 5) was found
3.14 not found!


--求交集--
>>> seq1="spam"
>>> seq2="scam"
>>> res=[]		# 开始为空
>>> for x in seq1:	# 扫描第一个序列
...     if x in seq2:	# 是否为公共项？
...             res.append(x)	# 向结尾添加结果
...
>>>
>>> res
['s', 'a', 'm']
>>>


--range和计数循环--
>>> range(5),range(2,5),range(0,10,2)
([0, 1, 2, 3, 4], [2, 3, 4], [0, 2, 4, 6, 8])

>>> x='spam'
>>> for item in x:	# 简单的循环
...     print item,
...
s p a m


>>> i=0
>>> while i < len(x):	# while循环
...     print x[i],
...     i=i+1
...
s p a m




----python读取和写入数据----
一、用Python创建一个新文件，内容是从0到9的整数, 每个数字占一行
>>> f=open('f.txt','w')
>>> for i in range(0,10):
...     f.write(str(i)+'\n')
...
>>> f.close()
whwu@master:~/script/python> cat f.txt
0
1
2
3
4
5
6
7
8
9

二、文件内容追加，从0到9的10个随机整数：
>>> import random
>>> f=open('f.txt','a')
>>> for i in range(0,10):
...     f.write(str(random.randint(0,9)))
...
>>> f.write('\n')
>>> f.close()
>>>
whwu@master:~/script/python> cat f.txt
0
1
2
3
4
5
6
7
8
9
3314668039