Function Nesting: How to Define Another Function Inside a Function in Python?
Python function nesting refers to defining an inner function within an outer function, which can hide functionality or implement complex logic. It has two calling methods: one is to directly call the inner function within the outer function; the other is to have the outer function return the inner function object for external invocation. The scope of the inner function is limited to the outer function. It can access the parameters or local variables of the outer function, but the outer function cannot access the local variables of the inner function, which is a core feature of nesting. Common uses of function nesting include implementing closures (where the inner function retains the state of the outer function) and decorators (which add additional functionality to functions, such as timing and logging). It enables code modular encapsulation and temporary state preservation, serving as a foundation for advanced Python features like closures and decorators. Beginners can start with nested calls and scope rules to gradually master its application in development.
Read MoreScope Mini Lesson: Local and Global Scopes of Python Variables
In Python, scoping determines the access range of variables, mainly divided into two types: local and global. **Local Scope**: Variables defined inside a function are only valid within that function (e.g., `age = 18`). If a variable with the same name as a global variable is defined inside a function, it will be treated as a local variable first (e.g., `x = 200` overwrites the global `x=100`, but the global `x` remains 100 externally). **Global Scope**: Variables defined outside a function are accessible throughout the entire program (e.g., `name = "Xiao Ming"`). There is no issue with direct access. However, if a function intends to modify a global variable, it must be declared with `global` (e.g., `global score`); otherwise, Python will mistakenly treat it as a local variable (e.g., `score=90` does not modify the original global value of 80). **Nested Functions**: The inner function can access the local variables of the outer function. When modifying these variables, the `nonlocal` declaration is required (e.g., `nonlocal outer_var`). Summary of Rules: Local scope is limited to the function, global scope spans the entire program; use `global` to modify global variables and `nonlocal` to modify outer local variables. Proper use of scoping can avoid variable conflicts and enhance code readability.
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