Being skilled in Python comes with an understanding and knowledge of using various structures and features. One such structure is the nested function. Just as the name implies, a nested function is a function within another function.
Nested functions can leverage variables from the enclosing function, leading to a coding pattern called closure. This tutorial is about writing nested functions in Python.
Step 1: Understanding Basic Python Function
The concept of nesting functions revolves around basic function definitions. Writing functions in Python involves the use of the def keyword. Here is an example:
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def greet(): return "Hello, World" greet() |
In the code above, a function named greet is defined. It returns the string “Hello, World” when called.
Step 2: Writing a Nested Function
Writing a nested function is diving a bit deeper. Let’s consider an example:
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def outer_func(): message = 'Hello, World' def inner_func(): print(message) return inner_func() outer_func() |
In the code above, we wrote a nested function, inner_func, which is nested within an outer_func. The inner_func prints out the message variable which is local to the outer_func.
Step 3: Utilizing Closure in Python
Closure is a record that stores a function together with an environment—a mapping associating each free variable of the function with the value or storage location. To understand this, let’s modify the code from Step 2:
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def outer_func(): message = 'Hello, World' def inner_func(): print(message) return inner_func new_func = outer_func() new_func() |
In this case, even after the outer function had returned, the inner function still had access to the ‘message’ variable. This ability is what makes the concept of closure very useful.
Step 4: Practice and Understand Scope in Nested Functions
It’s very important to understand the scope of variables in nested functions. A practice session on coding nested functions in Python will deepen the understanding of nested functions and variable scope.
Full code from this tutorial
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def outer_func(): message = 'Hello, World' def inner_func(): print(message) return inner_func new_func = outer_func() new_func() |
Conclusion
Understanding and being able to write nested functions in Python is a valuable skill in Python programming. A nested function can access variables from the enclosing function, thus, leading to a specific feature in Python known as closure. It’s recommended to always practice to master these concepts.