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Updated on 2025-04-18

Detailed explanation of the usage of self and parent parameters in Python methods

Usage of self and parent parameters in Python methods

Hello everyone! Today we will talk about a common but potentially confusing topic in Python: self and parent in method parameters. If you're new to Python or are confused about both, don't worry! In this blog, I will explain their meaning, function and practical applications step by step in three chapters to help you understand them thoroughly. Let's get started!

Chapter 1: Revealing the secret of self - the necessary parameters for example methods

In Python classes, you will often see that the first parameter when defining a method is self, such as the following example:

class Dog:
    def __init__(self, name):
         = name

    def bark(self):
        print(f"{} says woof!")

When called, it looks like this:

my_dog = Dog("Buddy")
my_dog.bark()  # Output: Buddy says woof!

What is self ?

Simply put,selfyesReferences to the current instance. When you create an object (such asmy_dog) and then call its method,selfIt represents the object itself. It lets the method know "which instance am I operating".

Why do you need self?

  • Distinguish instances: If you create multipleDogObject (such asDog("Buddy")andDog("Max")), each object has its ownnameAttributes.selfMake sure that the method operates the correct example. For example, callmy_dog.bark()hour,selfPoint tomy_dog, so the output name is"Buddy"。
  • Access properties and methods:passself, the method can access the attributes of the instance () or call other methods. This is the basis for Python to implement object state management.
  • Explicit design of Python: Unlike some languages ​​(such as Java'sthisImportant), Python requires explicit writingself. This makes the code clearer and developers can tell at a glance that the method is operating the instance.

How it works

When you callmy_dog.bark()When Python actually executes this behind it:

(my_dog)

here,my_dogIt is automatically passed to the first parameterbarkMethod, and this parameter isself。

summary

selfIs a required parameter for Python instance method, which represents the instance of the method itself. Noself, the method cannot know which object data it is operating on. By understanding this, you will master the basics of Python classes!

Chapter 2: Explore parent - Customized hierarchical parameters

compared toself，parentIt appears much less frequently in Python methods, and it is not a language built-in requirement. Then why are there some codes?parentWhat about the parameters? let's see.

Common scenarios of parent

parentUsually introduced by developers according to programming needs, representing the relationship between an object and its "parent object". Here are some typical situations:

  1. Tree structure or hierarchical relationship
    In a tree structure (such as a file system or a family tree), each node may need to know its parent node. At this time,parentCan appear as a parameter or attribute. Look at this example:

class TreeNode:
    def __init__(self, name, parent=None):
         = name
         = parent  # Save parent node reference         = []

    def add_child(self, child_name):
        child = TreeNode(child_name, parent=self)
        (child)

  • Here, eachTreeNodeObject passedparentThe parameter saves its parent node to form a hierarchy.

  • Nested classes
    When one class is nested in another, the inner class may need to access instances of the outer class. This can be usedparentParameter passing outer instance:

class Outer:
    def __init__(self):
         = (self)

    class Inner:
        def __init__(self, parent):
             = parent  # Save the outer instance

  • Special usage in inheritance (uncommon)In inheritance, subclasses are usually usedsuper()Access the parent class method. However, in some custom scenarios, developers may useparentRepresents an instance of the parent class. However, this usage is not recommended becausesuper()It is already strong enough.

Difference between parent and self

  • self: Always pointing to the current instance, is a built-in convention for Python.
  • parent: Point to another related object (usually the parent object), which is defined by the developer based on needs.

summary

parentNot a standard parameter for Python, but a design choice in specific scenarios. It is often used to represent hierarchical relationships between objects, such as tree structures or nested classes. Whether to useparent, it depends entirely on your program logic.

Chapter 3: Practical drills - Examples and best practices

After the theory is finished, let’s deepen our understanding through actual code!

Example 1: Simple class using self

class Car:
    def __init__(self, make, model):
         = make
         = model

    def display_info(self):
        print(f"This car is a {} {}.")

# usemy_car = Car("Toyota", "Corolla")
my_car.display_info()  # Output: This car is a Toyota Corolla.

here,selfletdisplay_infoMethods can access instancesmakeandmodelAttributes.

Example 2: Using parent’s tree structure

class TreeNode:
    def __init__(self, name, parent=None):
         = name
         = parent
         = []

    def add_child(self, child_name):
        child = TreeNode(child_name, parent=self)
        (child)

    def display(self, level=0):
        print("  " * level + )
        for child in :
            (level + 1)

# useroot = TreeNode("Root")
root.add_child("Child1")
root.add_child("Child2")
[0].add_child("Grandchild1")
()
# Output:# Root
#   Child1
#     Grandchild1
#   Child2

In this tree structure,parentParameters help each node remember its parent node.selfis used to manage the properties and behavior of each node.

Best Practices

  • Always useself: In the example method,selfIt is a must, don’t forget to write it!
  • Use with cautionparent: Use only when you need to clarify the hierarchical relationshipparent, otherwise it will complicate the code.
  • Stay clear: Be intuitive to name to avoid confusionselfandparentThe role.

Summarize

  • self: The soul of Python instance method, representing the current instance, is a bridge to access object data and behavior.
  • parent: Custom parameters, used to represent a certain relationship between objects (usually a parent-child relationship), which is useful in specific scenarios.

Hope this blog will help you understandselfandparentdoubt! With these masters, your Python object-oriented programming will take a step further.

This is the introduction to this article about the detailed explanation of the usage of self and parent parameters in Python methods. For more related content on Python self and parent, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!