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 heredef 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 heredef 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 heredef 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, inprintme(); TypeError: printme() takes exactly 1 argument (0 given)
2、指定参数：
#!/usr/bin/python# Function definition is heredef 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 heredef 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: mikiAge 50 Name: miki Age 35
4、动态参数： *args **kwargs
#!/usr/bin/python# Function definition is heredef 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 heresum = 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 heredef 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/pythontotal = 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