> a= 'py'
> b= 'thon'
> a+b
'python'

> a=1
> type(a)
<type 'int'> #a是整数
> b="1"
> type(b)
<type 'str'> #b是字符串
> print "one is %d"%a
one is 1
> print "one is %d"%b  #报错了，这个占位符的位置应该放整数，不应该放字符串。
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
TypeError: %d format: a number is required, not str

> print "one is %s"%b
one is 1
> print "one is %s"%a  #字符串是包容的
one is 1

> a = "py"
> b = "thon"
> print "%s%s"%(a,b) #注

> a = "My name is LaoQi. I like python and can teach you to learn it."
> print a
My name is LaoQi. I like python and can teach you to learn it.
> b = a
> print b
My name is LaoQi. I like python and can teach you to learn it.
> print a
My name is LaoQi. I like python and can teach you to learn it.

> a="hello"
> len(a)
5

> m = len(a) #把结果返回后赋值给一个变量
> m
5
> type(m)  #这个返回值（变量）是一个整数型
<type 'int'>

S.upper() #S中的字母大写
S.lower() #S中的字母小写
S.capitalize() #首字母大写
S.istitle() #S是否是首字母大写的
S.isupper() #S中的字母是否便是大写
S.islower() #S中的字母是否全是小写

> a = "Hello,World"
> a.upper()   #都是大写
'HELLO,WORLD'
> a.lower()   #都是小写
'hello,world'
> a.capitalize()  #首字母大写，其余小写
'Hello,wold'
> a.istitle()   #首字母是否是大写，如果是返回True,不是返回False
True
> a
'Hello,Wold'
> b="hellow,world"
> b.istitle()   #首字母不是大写，返回false
False
> a.islower()   #是否字符串中都是小写，如果是返回true，不是返回false
False
> b.islower()
True