Introduction to the function parameters of Python

Types of parameters for Python:

General parameters

Default parameters

Dynamic parameters

General parameters

Include: Formal parameters and arguments

A formal parameter is a form argument that is simply written in a function and is not assigned and called.

An argument is a parameter that is used when executing a function, and it is assigned in memory

Example:

Test (TXT): Txt,test ()

Output Result: Hello this is a test

Here txt is the formal parameter, ' hello ' is the argument

Default Parameters :

Requirements for Default parameters:

1, does not pass, then uses the default value,

2. The default parameter must be placed at the end of the parameter list

Calculation (x,y,z=): X+y+zcalculation (,) calculation (,,)

Output results

6

7

The default value for Z is 3, and when z is not assigned, x+y+z=1+2+3=6, when assigned to Z 4 o'clock, x+y+z=

dynamic parameter One : A *

Dynamic parameters have no limit on the number of parameters, can accept any parameter

>>> def func (*arg): ... print arg ... >>> func () () >>> func (1) (1,) >>> func (1, 2) >>> func (1, 2, 3)

From the above example, the dynamic parameter can accept 0 or more parameters, each of which is an element in the tuple.

What if the passed parameter itself is a tuple?

>>> a= (11,22,33) >>> func (A) ((11, 22, 33),)

You can see that the tuple itself becomes an element in the tuple, as it is passed into the function as a parameter.

If you do not want this, the result is (11,22,33) This tuple, how to achieve? The answers are as follows:

>>> func (*a) (11, 22, 33)

Add a * before the tuple.

Change a tuple to a list

>>> a[11, 33]>>> func (*a) (11, 22, 33)

Use subscript to get dynamic parameters

>>> def func (*args): ... print args[0]...>>> func (11,22,33) 11

Dynamic parameter two: two *

The function of this dynamic parameter is required for the parameter, and the passed parameter must be

K=value this, get the result is the dictionary

>>> def func (**args): ... func (11,22) ...>>> def func (**args): ... print args...>>> func (1 , Traceback (most recent): File ' <stdin> ', line 1, in <module>typeerror:func () takes exactly 0 a Rguments (2 given) >>> func (k=1) {' K ': 1}>>> func (k=1,k1=22) {' K ': 1, ' K1 ': 22}

Can see the direct 1,22 times wrong. But there's no problem with passing k=1 this form of argument.

You can also pass a dictionary

>>> Dic1 = {' name ': ' Zeng ', ' Age ':28}>>> func (**dic1) {' Age ': ' ' name ': ' Zeng '}>>> func (dic1 ) Traceback (most recent): File "<stdin>", line 1, in <module>typeerror:func () takes exactly 0 Argu ments (1 given)

Note: When passing a dictionary, you also need to add * *, otherwise error

Dynamic parameter three :

The two dynamic parameters above, the first (one *) can only accept parameters of a single value, and the second (two *) can only accept parameters of the form Key=value. The third parameter is the dynamic parameter which can accept the two formal parameters.

>>> def func (*args,**kargs): ... print Kargs ... print args...>>> func (11,22) {} (one, all) >>> ; Func (name= ' Zeng ') {' name ': ' Zeng '} () >>> func (name= ' Zeng ', age=28) {' Age ': +, ' name ': ' Zeng '} () >>> Func (11,22,name= ' Zeng ', age=28) {' Age ': +, ' name ': ' Zeng '} (11, 22)

A typical example of a third dynamic parameter is the Format function

>>> str = ' I am {0},age {1} ' >>> Str.format (' Zeng ', +) ' I am zeng,age 28 '

This notation uses only one of the three dynamic parameters.

>>> str = ' I am {name},age {age} ' >>> Str.format (name= ' Zeng ', age=28) ' I am zeng,age 28

' This notation uses two of the dynamic parameters.

This article is from the "Zengestudy" blog, make sure to keep this source http://zengestudy.blog.51cto.com/1702365/1825873

Introduction to the function parameters of Python