__closure__ magic function in Python

Python is famous for its straightforwardness, readability, and a number of capable highlights that empower developers to type in clean and productive code. Among these highlights is the magic, which permits you to imitate built-in behavior or execute custom functionality. While Python does not have a __closure__ magic method, it does have a trait called __closure__ related to function objects. In this article, we are attending to explore the concept of closures in Python, examine the __closure__ property, and learn how to utilize it successfully in your code.

Section 1: Understanding Closures in Python

In Python, functions are first-class citizens, meaning they can be allocated to variables, passed as arguments, or returned from other functions. A closure may be a settled work that captures and holds the values of the variables in its containing function's scope, indeed after the external work has completed execution. Closures permit you to characterize behavior based on the captured variables and make function factories.

The primary elements of closure in Python are −

  • A nested function that references one or more variables from its containing function.

  • The containing (or outer) function, returns the nested function.

Section 2: The closure Attribute

In Python, function objects have a __closure__ attribute that stores information about the captured variables from the containing function's scope. The __closure__ attribute is a tuple containing cell objects, where each cell object represents a captured variable. In the event that a function does not capture any variables from its containing function, its __closure__ attribute will be None.

To get to the value of a captured variable inside a cell protest, you'll be able to utilize the cell_contents attribute of the cell object.

Section 3: Examples of Closures and the Closure Attribute

Example 1: Basic Closure

  • Define outer_function with a parameter x.

  • Define a nested function inner_function with a parameter y that returns the sum of x and y.

  • Return inner_function from outer_function.

  • Call outer_function(10) to create a closure that captures x=10.

  • Call the closure with argument 5. The closure calculates the sum 15.

def outer_function(x):
   def inner_function(y):
      return x + y
   return inner_function
closure = outer_function(10)
result = closure(5)



Example 2: Inspecting the closure Attribute

  • Define outer_function and inner_function as in Example 1.

  • Call outer_function(10) to create a closure that captures x=10.

  • Examine the __closure__ attribute of the closure, which is a tuple containing a single cell object representing x.

  • Access the value of x using the cell_contents attribute of the cell object, which is 10.

def outer_function(x):
   def inner_function(y):
      return x + y
   return inner_function

closure = outer_function(10)
print(closure.__closure__)  # Output: (<cell at 0x7f8f0c3e0ee0: int object at 0x55e3ed2d44a0>,)


(<cell at 0x7fb45fa40310: int object at 0x7fb45fb18210>,)

Section 4: Use Cases and Best Practices

  • Use closures to create function factories - Closures are a powerful way to create function factories that generate functions with specific behavior based on the captured variables. By leveraging closures, you can create reusable and modular code.

  • Inspect captured variables with the closure attribute - The __closure__ attribute can be a valuable debugging tool when working with closures, as it allows you to inspect the captured variables and their values. By understanding the contents of the __closure__ attribute, you can gain insights into the behavior of your closures and identify potential issues.

  • Be cautious with mutable captured variables - When a closure captures a mutable variable, such as a list or dictionary, modifying the variable within the closure will affect the original variable in the containing function's scope. Be mindful of this behavior to prevent unintended side effects in your code.

  • Avoid utilizing global variables - Closures can offer assistance to reduce the dependence on global variables by encapsulating the specified factors inside the scope of the containing function. This leads to cleaner, more valid, and less error-prone code.


Closures are an effective feature in Python that permits you to make nested functions that capture and hold variables from their containing function's scope. By understanding closures and the __closure__ attribute, you can create function factories, write modular code, and effectively debug your closures. While Python does not have a __closure__ magic method, the __closure__ attribute plays an important role in working with closures and understanding their behavior. By embracing closures and the __closure__ attribute, you can harness their power to write more efficient, organized, and maintainable Python code.

Updated on: 08-May-2023


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