函数返回值：


  1)函数被调用后会返回一个指定的值


  2)函数调用后默认返回None


  3)return返回值


  4)返回值可以是任意类型


  5)return执行后，函数终止


  6)区分返回值和打印


user1@ubuntu:~$ python
Python 2.7.3 (default, Sep 26 2013, 20:03:06) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> def f(x):
...     print x
... 
>>> f(0)
0
>>> def f(x,y):
...     print x+y
... 
>>> f(2,3)
5
>>> f('i love','you')
i loveyou
>>> f('i love',' you')
i love you
>>> z=f(2,3)
5
>>> z
>>> print z
None
>>> sum([1,2,3,4,5])
15
>>> z = sum([1,2,3,4,5])
>>> z
15
>>> def f(x,y):
...     print "welcome !"
...     return x+y
... 
>>> f(2,3)
welcome !
5
>>> z=f(2,3)
welcome !
>>> z
5
>>> def f():
...     return "hello"
... 
>>> f()
'hello'
>>> x = f()
>>> x
'hello'
>>> print x
hello
>>> def f():
...     return range(10)
... 
>>> f()
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> def f():
...     return "one"
...     return "two"
... 
>>> f()
'one'
>>> def f(x,y):
...     if x>y:
...             return 1
...     if x<y:
...             return -1
...     if x==y:
...             return 0
... 
>>> f(2,3)
-1
>>> f(2,1)
1
>>> f(2,2)
0
>>> def f(x,y):
...     if x>y:
...             return 1
...     if x<y:
...             return -1
...     return 0
... 
>>> f(1,2)
-1
>>> def f(x,y):
...     if x<y:
...             return -1
...     print "hello world"
... 
>>> f(1,4)
-1
>>> f(4,1)
hello world
>>> z = f(4,1)
hello world
>>> z
>>> print z
None
>>> z = f(1,4)
>>> z
-1
>>> print z
-1
>>>