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Python中能直接import self吗?

Of course. This is an excellent question that gets to the heart of what the self keyword represents in Python.

Python中能直接import self吗?-图1
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Let's break it down. The short answer is:

You cannot and should not import self in Python.

The keyword self is not a module or a class that you can import. It's a special, built-in parameter name used in instance methods of a class.


The Detailed Explanation: What is self?

Think of self as a reference to the specific object (or instance) that is currently being worked on. When you create an object from a class, that object needs a way to refer to its own data (attributes) and its own methods.

Python中能直接import self吗?-图2
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self is that reference.

Let's look at a simple example:

class Dog:
    # This is the constructor method, called when you create a new Dog object
    def __init__(self, name, breed):
        # 'self' refers to the specific Dog object being created
        # We are setting an attribute 'name' on that object
        self.name = name
        self.breed = breed
        print(f"A new dog named {self.name} has been created!")
    # This is an instance method
    def bark(self):
        # 'self' refers to the Dog object that called this method
        # We can access its attributes using self
        return f"{self.name} says: Woof!"
# --- Let's use the class ---
# Create an instance (an object) of the Dog class
# Python automatically passes the instance as the first argument to __init__
my_dog = Dog("Rex", "German Shepherd")
# Create another instance
your_dog = Dog("Buddy", "Golden Retriever")
# Now, call the bark() method on each object
# Python automatically passes the instance as the first argument to bark()
print(my_dog.bark())
print(your_dog.bark())

How it Works Behind the Scenes:

When you write this code:

my_dog.bark()

Python secretly does this:

Python中能直接import self吗?-图3
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Dog.bark(my_dog)

It takes the method bark from the Dog class and calls it, passing my_dog as the first argument. That's why the self parameter in the method definition def bark(self): receives the my_dog object.


Why You Can't import self

  1. It's a Keyword, Not a Module: Python has a set of reserved keywords (like for, if, try, class, def). self is not on that list, but it functions like one in the context of classes. It's a conventional name for the first parameter of an instance method. You could technically name it something else (like this or me), but it is a very strong convention to always use self.

  2. It's Not a Global Object: self only has meaning inside an instance method. It doesn't exist in the global scope. You can't try to access it outside of a class method, just as you can't access a local variable from outside its function.

  3. It's Dynamically Supplied: As shown above, Python provides the self argument for you automatically when you call an instance method. You don't need to import it because it's already there in the context where it's needed.


Common Confusion: self vs. __name__

A common point of confusion for beginners is mixing up self with __name__. Let's clarify the difference.

Keyword/Variable What it is When it's Available Example
self A reference to the current object instance. Only inside instance methods of a class. self.name
__name__ A special dunder (double underscore) variable that holds the name of the current module. In any Python file/module. if __name__ == "__main__":

Example of __name__:

Create a file named my_module.py:

# my_module.py
print("This code will always run when the module is imported.")
def my_function():
    print("my_function was called.")
if __name__ == "__main__":
    print("This code only runs when the file is executed directly.")
    my_function()

Now, run it from your terminal:

python my_module.py

Output:

This code will always run when the module is imported.
This code only runs when the file is executed directly.
my_function was called.

Now, create another file that imports it:

# main_script.py
import my_module
print("main_script is now running.")

Run main_script.py: Output:

This code will always run when the module is imported.
main_script is now running.

Notice the if __name__ == "__main__": block did not run. This is because when my_module is imported, its __name__ variable is set to the string "my_module", not "__main__".


Summary

Concept Description Can you import it?
self A special parameter in an instance method that refers to the object itself. No. It's a built-in convention, not a module.
__name__ A special variable that holds the name of the current module. No. It's a built-in variable, not a module.
A Module A file containing Python code (e.g., import math, import requests). Yes. This is what the import statement is for.

So, in short: forget about importing self. Just use it as the first parameter in your instance methods to access the object's attributes and other methods.

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