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Table of Contents
What exactly does dir() show on the class?
Why do you see inherited content?
How to quickly find what you define?
Suggestions on practical usage
Home Backend Development Python Tutorial Python `dir()` function on class objects

Python `dir()` function on class objects

Jul 04, 2025 am 03:25 AM
python dir() function

The dir() function is used in Python to list all properties and methods of a class, including inherited members. When you use dir() on a class, it returns all available names of the class, such as defined methods, properties, and built-in properties automatically added by Python such as __doc__, __module__, __dict__, etc. By default, these built-in properties are displayed as default values. If the class has an inheritance relationship, dir() will also display the methods and properties in the parent class, because its search scope includes the current class and all its base classes. In order to quickly identify the content you define, you can compare the dir() output of the empty class or use __dict__ to view the properties and methods defined by the current class itself, so as to exclude the impact of inherited content. In practical applications, dir() is suitable for quickly viewing the operations supported by the class during debugging, troubleshooting spelling errors or overrides, and combining help() or __mro__ to understand the inheritance structure.

Python `dir()` function on class objects

When you use the dir() function to view a class object in Python, you may see a bunch of results that don't look very intuitive. This is actually quite common, especially for people who are new to Python-like mechanisms, they may be a little confused. Here we will directly talk about the key point: dir() will list all attributes and methods of the class, including those inherited.

Python `dir()` function on class objects

What exactly does dir() show on the class?

Simply put, as long as you pass a class to dir() , it will return all the names (property name, method name, etc.) that the class can use. for example:

Python `dir()` function on class objects
 class MyClass:
    def method(self):
        pass

print(dir(MyClass))

In addition to method you define yourself, there will also be a bunch of "double underscore" names like __doc__ , __module__ , and __dict__ in the output. These are built-in properties that Python automatically adds. If you haven't changed these contents, they usually display default values.

In addition, if your class is inherited from another class, the methods in the parent class will also appear in the result of dir() . This is why sometimes you will see some methods that you haven't written are listed.

Python `dir()` function on class objects

Why do you see inherited content?

Because dir() not only depends on what the current class defines itself, it also looks up along the inheritance chain. For example, you write this:

 class Parent:
    def parent_method(self):
        pass

class Child(Parent):
    def child_method(self):
        pass

At this time, execute dir(Child) and you will find that there are both child_method and parent_method . This is because Child inherits Parent , so its "available members" naturally include the parent class.

This is sometimes misunderstood, thinking that it was written by the current class itself, but in fact it can only be called. So when looking at the result of dir() you should pay attention to what inherited it.


How to quickly find what you define?

If you want to quickly find out what you added by yourself from the results of dir() , there are several ways:

  • You can first look at the dir() output of the empty class and record which items are default.
  • Then dir() your own class and compare it to see which ones are available.
  • Or you can use __dict__ to view the properties defined by the current class itself:
 print(MyClass.__dict__.keys())

This will not contain inherited content, and only display the properties and methods defined by the current class itself. Although the output form is different, it is more accurate.


Suggestions on practical usage

  • During debugging , use dir() to quickly view what operations a class supports, so as to save document translation.
  • When troubleshooting problems , if a method does not take effect, you can use dir() to see if it is spelled wrongly or is overwritten.
  • When you want to understand the inheritance structure , you can better understand the inheritance relationship by combining help() or printing .__mro__ .

Basically that's it. dir() is a very practical gadget. If you use it too much, you will know how to avoid interfering information and grasp the key points.

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