Python functions

　　Tissue function is good, reusable, code segments used to implement a single, or the associated function. Function module of the application can be improved, and code reuse. Python provides many built-in functions, such as print (). You can also create your own functions, which are called user-defined functions.

The definition of a function

In function block def beginning keyword, followed by the function identifier name and parentheses () .
Any incoming parameters and arguments must be placed in the middle of parentheses. Between parentheses may be used to define the parameters.
The first statement function can be selectively used documentation string - for storing function instructions.
Function contents colon starting and retracted .
return [Expression] End function, selectively returns a value to the caller. Return without an expression equivalent to return None.

grammar:

DEF functionName (Parameters):
    " function _ Document string " 
   function_suite 
   return [expression The]

Example:

# Create a function 
>>> DEF MyFirstFunction ():
     Print ( ' ! This is the first function I created ' )
     Print ( ' ! Tan baby ' )
 # call the function 
>>> MyFirstFunction () 
This is the first I've created functions! 
Tan Baby!

Function parameters:

　　In python, belong to the object type, the variable type is not:

a=[1,2,3]
a="Runoob"

PS: the above code, [1,2,3] type is List, "Runoob" is of type String, and the variable is not a type, she is just an object reference (a pointer) can be List type object, you can point to a String object.

# If you set the function parameters when calling need to fill out the parameter value, or will be error 
>>> DEF MySecondFunction (name):
     Print (name + ' the I Love by You ' )

    
 >>> MySecondFunction () 
Traceback (MOST recent Results Last Call ): 
  File " <pyshell # 10> " , Line. 1, in <Module1> 
    MySecondFunction () 
TypeError: MySecondFunction () Missing . 1 Positional required argument: ' name ' 
>>> MySecondFunction ( ' tanbaobao ' ) 
tanbaobaoI by You Love

#Define add function

>>> def add(num1,num2):
result = num1 + num2
print(result)

>>> add(2,3)
5

Parameter (parameter) and arguments (argument):

>>> DEF MySecondFunction (name):
     ' function definition process is called parameter name ' 
    # just as he forms, represents a parameter to occupy a position 
    Print ( ' passed in ' + name +   ' call argument, because he specific parameter values are ' )

 >>> MySecondFunction ( ' tanbaobao ' )
 ' tanbaobao is passed in argument, because he is the specific parameter value '

Keyword arguments:　

　　关键字参数和函数调用关系紧密，函数调用使用关键字参数来确定传入的参数值。使用关键字参数允许函数调用时参数的顺序与声明时不一致，因为 Python 解释器能够用参数名匹配参数值。

　　如果没有加上关键字，则会按输入的内容进行索引，加上则按照关键字索引，会按参数上的顺序输出：

默认参数：

　　默认参数即定义了默认值的参数。调用函数时，默认参数的值如果没有传入，则被认为是默认值。

不定长参数（收集参数，可变参数）：

　　需要一个函数能处理比当初声明时更多的参数。这些参数叫做不定长参数，和上述2种参数不同，声明时不会命名。加了星号（*）的变量名会存放所有未命名的变量参数。

def functionname([formal_args,] *var_args_tuple ):
   "函数_文档字符串"
   function_suite
   return [expression]

PS：如果既有不定长参数，又有其他参数，建议将其他参数定义为默认参数，这样能减少出错。

# 定义可变参数，还有其他的参数
>>> def test(*params,other):
    print('参数长度：',len(params))
    print('第二个参数：',params[1])

# 调用的时候如果忘记设置其他参数的值会报错
>>> test(1,'谭酱',3.14,5,6,7,8)
Traceback (most recent call last):
  File "<pyshell#58>", line 1, in <module>
    test(1,'谭酱',3.14,5,6,7,8)
TypeError: test() missing 1 required keyword-only argument: 'other'
# 最好的建议是将其他参数设置为默认参数，这样就算忘记传参数，也不会报错
>>> def test(*params,other=2):
    print('参数长度：',len(params),other)
    print('第二个参数：',params[1])

    
>>> test(1,'谭酱',3.14,5,6,7,8)
参数长度： 7 2
第二个参数： 谭酱

Python Python function []