>>> 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