学步园

1 函数的定义：

语法：

def functionname( parameters ):


   "function_docstring"


   function_suite


   return [expression]



具体规则如下：

• Function blocks begin with the keyword def
  followed by the function name and parentheses ( ( ) ).

• Any input parameters or arguments should be placed within these
  parentheses. You can also define parameters inside these parentheses.

• The first statement of a function can be an optional statement - the documentation string of the function or docstring
  .

• The code block within every function starts with a colon (:) and is indented.

• The statement return [expression] exits a function, optionally
  passing back an expression to the caller. A return statement with no
  arguments is the same as
  return None.

2 函数传值和传引用：

All parameters (arguments) in the Python language are passed by
reference.
It means if you change what a parameter refers to within a
function, the change also reflects back in the calling function.

#!/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)

3 在函数中传递可变长度参数：

具体申明为：

The general syntax for a function with non-keyword variable arguments is this:

def functionname([formal_args,] *var_args_tuple ):


   "function_docstring"


   function_suite


   return [expression]



例子：

#!/usr/bin/python

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

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

输出为：

D:/>python test.py
Output is:
mmmm   10
Output is:
mmmm   70
60
50

4 匿名函数：

You can use the lambda

keyword to create small anonymous
functions. These functions are called anonymous because they are not
declared in the standard manner by using the def
keyword.

• Lambda forms can take any number of arguments but return just one
  value in the form of an expression. They cannot contain commands or
  multiple expressions.

• An anonymous function cannot be a direct call to print because lambda requires an expression.

• Lambda functions have their own local namespace and cannot access
  variables other than those in their parameter list and those in the
  global namespace.

• Although it appears that lambda's are a one-line version of a function, they are not equivalent to inline
  statements in C or C++, whose purpose is by passing function stack allocation during invocation for performance reasons.

Syntax:

The syntax of lambda
functions contains only a single statement, which is as follows:

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

Example:

Following is the example to show how lembda
form of function works:

#!/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 )

This would produce following result:

Value of total :  30


Value of total :  40

关于python函数中是传值还是传引用，我觉得应该是全部传递引用，只是在遇到某些不能修改的数据类型的时候，会表现为何传值一样的行为。

具体参见：

http://blog.csdn.net/winterTTr/archive/2008/06/27/2590741.aspx