Understanding the Meaning of Single and Double Underscore Before an Object Name in Python

Python Oop Naming Conventions Identifier

In Python, you might come across object names that start with either a single underscore (_) or a double underscore (__). These underscores have special meanings and conventions associated with them. Understanding these conventions can help you write cleaner, more readable code and avoid naming conflicts. In this article, we will explore the meaning of single and double underscores before an object's name in Python.

Single Underscore Before an Object Name

When a single underscore (_) is used before an object's name, it indicates that the object is intended to be treated as internal or private. However, this is merely a convention and does not enforce any access restrictions. It is a way for developers to signal to other developers that the object should not be accessed or modified from outside the class or module.

Here's an example:

class MyClass:
    def __init__(self):
        self._private_var = 10
        
    def _private_method(self):
        print("This is a private method")
        
    def public_method(self):
        print("This is a public method")
        
obj = MyClass()
print(obj._private_var) # Output: 10
obj._private_method() # Output: This is a private method
obj.public_method() # Output: This is a public method

In the above example, the single underscore (_) before the variable name and method name indicates that they are intended to be treated as private. However, it is still possible to access them from outside the class. It's important to note that names starting with a single underscore do not get imported by default when using the `from module import *` syntax.

Double Underscore Before an Object Name

When a double underscore (__) is used before an object's name, it invokes name mangling. Name mangling is a mechanism to make an object's attribute or method name unique to its class. It is used to avoid naming conflicts between attributes or methods of parent and child classes that have the same name.

Here's an example:

class ParentClass:
    def __init__(self):
        self.__private_var = 10
    
    def __private_method(self):
        print("This is a private method")
        
class ChildClass(ParentClass):
    def __init__(self):
        super().__init__()
        self.__private_var = 20
        
obj = ChildClass()
print(obj._ParentClass__private_var) # Output: 10
obj._ParentClass__private_method() # Output: This is a private method

In the above example, we have a parent class and a child class. Both classes have attributes and methods with the same name (__private_var and __private_method). When accessing these attributes or methods from outside their respective classes, we need to use the name mangling convention: _ClassName__attribute_or_method_name.

When to Use Single or Double Underscores

As mentioned earlier, using a single underscore before an object's name is a convention to indicate that it should be treated as internal or private. It is a way of communicating with other developers. However, it does not prevent the object from being accessed or modified directly.

On the other hand, using a double underscore before an object's name invokes name mangling. This is typically used when there is a possibility of naming conflicts between attributes or methods of parent and child classes. It ensures that the attribute or method is unique to its class.

It's important to note that using a single or double underscore before an object's name does not provide true encapsulation or access control in Python. It is still possible to access or modify the object if needed. It is up to the developer to follow naming conventions and respect the intentions behind these conventions.

Conclusion

Understanding the meaning of single and double underscores before an object's name in Python is crucial for writing clean, maintainable code. Single underscores indicate that an object is intended to be treated as internal or private, while double underscores invoke name mangling to prevent naming conflicts. By following these naming conventions, you can improve the readability of your code and avoid potential conflicts.

Remember, the use of underscores is a convention and does not provide strict access control. It is still possible to access or modify the objects if needed. Following the naming conventions and respecting the intentions behind them is crucial for writing high-quality Python code.

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