语法：

def functionname( parameters ):
   "function_docstring"
   function_suite
   return [expression]

例（定义一个函数）：

def printme( str ):
   "This prints a passed string into this function"
   print （str）
   return


调用函数：

#!/usr/bin/python

# Function definition is here
def printme( str ):
   "This prints a passed string into this function"
   print （str）
   return;

# Now you can call printme function
printme("I'm first call to user defined function!")
printme("Again second call to the same function")

执行结果返回：

I'm first call to user defined function!
Again second call to the same function



传参，往函数里面传递参数：
所有参数（参数）用Python语言通过引用传递。这意味着，如果你改变什么参数指的是在一个函数中，变化也反映在回调用函数。例如 -

#!/usr/bin/python

# Function definition is here
def changeme( mylist ):
   "This changes a passed list into this function"
   mylist.append([1,2,3,4]);
   print "Values inside the function: ", mylist
   return

# Now you can call changeme function
mylist = [10,20,30];
changeme( mylist );
print "Values outside the function: ", mylist

在这里，我们维持传递的对象，并在同一个对象附加的值(如：列表、元组、字典等)。因此，这将产生以下结果 -

Values inside the function:  [10, 20, 30, [1, 2, 3, 4]]
Values outside the function:  [10, 20, 30, [1, 2, 3, 4]]

　　1、普通参数：

#!/usr/bin/python

# Function definition is here
def printme( str ):
   "This prints a passed string into this function"
   print （str）
   return;

# Now you can call printme function
printme()

当我们执行时，会得到以下返回值，因为执行函数时，没有传入必要的参数

Traceback (most recent call last):
  File "test.py", line 11, in <module>
    printme();
TypeError: printme() takes exactly 1 argument (0 given)

　　2、指定参数：

#!/usr/bin/python

# Function definition is here
def printme( str ):
   "This prints a passed string into this function"
   print str
   return;

# Now you can call printme function
printme( str = "My string")                #指定需要传入的参数，执行结果得到:My string

　　3、默认参数：

#!/usr/bin/python

# Function definition is here
def printinfo( name, age = 35 ):
   "This prints a passed info into this function"
   print ("Name: ", name)
   print ("Age ", age)
   return;

# Now you can call printinfo function
printinfo( age=50, name="miki" )
printinfo( name="miki" )

  上面定义了传入的参数个数，其中age = 35(默认值)，我们看下执行结果，当没有指定参数传入时，默认显示则为35

Name:  miki
Age  50
Name:  miki
Age  35

　　4、动态参数：
　　　　　　*args
　　　　　　**kwargs

#!/usr/bin/python

# Function definition is here
def printinfo( arg1, *vartuple ):
   "This prints a variable passed arguments"
   print "Output is: "
   print arg1
   for var in vartuple:
      print var
   return;

# Now you can call printinfo function
printinfo( 10 )
printinfo( 70, 60, 50 )

我们传入了一个变量，跟一个元组，执行后得到

Output is:
10
Output is:
70
60
50

　　5、万能参数：
　　　　　　*args,**kwargs



lambda语法：

lambda [arg1 [,arg2,.....argn]]:expression

#!/usr/bin/python

# Function definition is here
sum = lambda arg1, arg2: arg1 + arg2;

 

# Now you can call sum as a function
print "Value of total : ", sum( 10, 20 )
print "Value of total : ", sum( 20, 20 )

　　执行得到以下结果：

Value of total :  30
Value of total :  40

return语句：

#!/usr/bin/python

# Function definition is here
def sum( arg1, arg2 ):
   # Add both the parameters and return them."
   total = arg1 + arg2
   print "Inside the function : ", total
   return total;

# Now you can call sum function
total = sum( 10, 20 );
print "Outside the function : ", total 

　　执行得到结果：

Inside the function :  30
Outside the function :  30

全局变量：
本地变量：

#!/usr/bin/python

total = 0; # This is global variable.
# Function definition is here
def sum( arg1, arg2 ):
   # Add both the parameters and return them."
   total = arg1 + arg2; # Here total is local variable.
   print "Inside the function local total : ", total
   return total;

# Now you can call sum function
sum( 10, 20 );
print （"Outside the function global total : ", total）

执行结果

Inside the function local total :  30
Outside the function global total :  0

　　本地变量声明全局变量