Python function call and parameter passing (example analysis)

In today’s article, we will learn about the knowledge related to python function calling and parameter passing. After we understand what a function is, what we need to understand is how python uses functions. After all, if you only know what a function is but don't know how to call a function in Python, then only knowing the definition of the function is of no use. Without further ado, let's start learning to call functions.

Function call: Defining a function only gives the function a name, specifies the parameters contained in the function, and the code block structure. Once the basic structure of this function is complete, you can execute it through another function call or directly from the Python prompt. The following example calls the printme() function:

#!/usr/bin/python
# -*- coding: UTF-8 -*-
 
# 定义函数
def printme( str ):
   "打印任何传入的字符串"
   print str;
   return;
 
# 调用函数
printme("我要调用用户自定义函数!");
printme("再次调用同一函数");

The output results of the above example are as follows:

我要调用用户自定义函数!
再次调用同一函数

This is quite simple, you only need to experiment with it to understand.

Next let’s talk about Parameter passing: In python, types belong to objects, and variables have no type.

Refer to the following coding:

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

(In the above code, [1,2,3] is List type, "Runoob" is String type, and variable a has no type , she is just a reference to an object (a pointer), which can be a List type object or a String type object.)

Changeable (mutable) and immutable (immutable) object

(In python, strings, tuples, and numbers are immutable objects, while list, dict, etc. are objects that can be modified.)

1. Immutable type: After the variable is assigned a=5, it is assigned a=10. Here, a new int value object 10 is actually generated, and then a points to it, and 5 is discarded, not changed. The value of a is equivalent to the newly generated a.

2. Variable type: variable assignment la=[1,2,3,4] and then assignment la[2]=5 will change the value of the third element of list la, but la itself has no It moves, but some of its internal values ​​are modified.

Parameter passing of python function:

1. Immutable type: C-like value passing, such as integer, string, tuple. For example, fun(a) only transfers the value of a and does not affect the a object itself. For example, modifying the value of a inside fun(a) only modifies another copied object and does not affect a itself.

2. Variable type: similar to c reference transfer, such as list, dictionary. For example, fun(la) will actually pass la. After modification, la outside fun will also be affected

(Everything in python is an object, strictly speaking We can't say whether to pass by value or by reference. We should say passing immutable objects and passing mutable objects.)

Python passing immutable objects instance:

#!/usr/bin/python
# -*- coding: UTF-8 -*-
 
def ChangeInt( a ):
    a = 10
 
b = 2
ChangeInt(b)
print b # 结果是 2

(There is int object 2 in the instance, and the variable pointing to it is b. When passed to the ChangeInt function, the variable b is copied by value. Both a and b point to the same Int object. In a =10, create a new int value object 10 and let a point to it.)

Python passes the variable object instance:

#!/usr/bin/python
# -*- coding: UTF-8 -*-
 
# 可写函数说明
def changeme( mylist ):
   "修改传入的列表"
   mylist.append([1,2,3,4]);
   print "函数内取值: ", mylist
   return
 
# 调用changeme函数
mylist = [10,20,30];
changeme( mylist );
print "函数外取值: ", mylist

Instance The object passed into the function and the object with new content added at the end use the same reference, so the output result is as follows:

函数内取值:  [10, 20, 30, [1, 2, 3, 4]]
函数外取值:  [10, 20, 30, [1, 2, 3, 4]]

The above is what I want to explain today, how to call the function, and python parameter passing. Although the above knowledge points give examples, you still need to try it yourself. After all, if you don't do it yourself, it is just like talking on paper. Hands-on practice is the best way and way to verify what you have learned. Finally, I also hope that this article can bring some help to you who are learning python
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