6.3 Variable scope
2 min read•june 24, 2024
Variable in Python determines where variables can be accessed within a program. Understanding and local scopes is crucial for writing efficient and organized code. This knowledge helps prevent naming conflicts and ensures proper data .
The 'global' keyword allows functions to modify variables in the . Advanced concepts like lexical scoping and closures further enhance your ability to manage variable accessibility and lifetime in Python programs.
Variable Scope in Python
Variable scope and accessibility
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- Variable scope determines where a variable can be accessed within a program
- Variables defined outside any have making them accessible from anywhere in the program, including inside functions (main.py)
- Variables defined inside a function have meaning they are only accessible within the function where they are defined
- Not accessible outside the function or in other functions (my_function())
- Python first looks for a variable in the , then in the enclosing scope if any (nested functions), and finally in the global scope
- This hierarchical lookup process is known as
Global vs local variables
- Global variables are defined outside any function
- Accessible from anywhere in the program, including inside functions (count = 0)
- Can be read inside functions without any special declaration
- Modifying global variables inside a function requires the 'global' keyword
- Local variables are defined inside a function
- Accessible only within the function where they are defined (x = 5)
- Not accessible outside the function or in other functions
- Function parameters are also considered local variables (def greet(name))
- Local variables are created when the function is called and destroyed when the function ends
Global keyword for scope modification
- The 'global' keyword allows a function to modify a variable defined in the global scope
- Without the 'global' keyword, assigning a value to a variable inside a function creates a new local variable with the same name
- To modify a global variable inside a function:
- Use the 'global' keyword followed by the variable name at the beginning of the function
- After declaring a variable as global, any assignment to that variable inside the function will modify the global variable
- Example:
x = 10 def modify_global(): global x x = 20 modify_global() print(x) # Output: 20
Advanced scope concepts
- : Python uses lexical scoping, where the scope of a variable is determined by its position in the source code
- : The period during which a variable exists in memory and is accessible
- : A function object that remembers values in enclosing scopes even if they are not present in memory
Key Terms to Review (21)
Built-in function: A built-in function is a function provided by Python that is always available and does not require any additional imports. Examples include functions like len(), max(), min(), and abs().
Built-in Scope: Built-in scope refers to the accessibility and visibility of variables within the context of a programming language's built-in functions, modules, or objects. It determines the level of access and control programmers have over these pre-defined entities.
Class: A class is a blueprint for creating objects, encapsulating data for the object and methods to manipulate that data. It allows for the creation of user-defined data structures.
Class: In the context of programming, a class is a blueprint or template that defines the structure and behavior of objects. It serves as a blueprint for creating objects, which are instances of the class, and encapsulates data and functionality within a cohesive unit.
Closure: Closure is a function that has access to variables from an outer function, even after the outer function has finished executing. It allows the inner function to 'remember' and continue to use the variables from the outer function's scope, even after the outer function has returned.
Encapsulation: Encapsulation is a fundamental concept in object-oriented programming (OOP) that involves bundling data and methods into a single unit, known as a class. It is the mechanism that allows objects to hide their internal implementation details from the outside world, providing a well-defined interface for interacting with the object.
Function: A function is a reusable block of code that performs a specific task or operation. It is a fundamental concept in programming that allows for the modularization and organization of code, promoting efficiency, readability, and maintainability.
Global: The term 'global' in programming refers to the scope or visibility of a variable. A global variable is a variable that is accessible throughout the entire program, regardless of the function or block of code it is defined in.
Global scope: Global scope refers to variables that are defined outside of any function and can be accessed from anywhere in the code. These variables retain their values throughout the lifetime of the program.
Global Scope: Global scope refers to the accessibility and visibility of variables that are defined outside of any function or class in a Python program. These variables are available throughout the entire code, making them accessible from anywhere within the program.
LEGB Rule: The LEGB rule is a fundamental concept in Python that governs the scope and visibility of variables. It stands for Local, Enclosing, Global, and Built-in, and it determines the order in which Python searches for variables within a program.
Lexical Scope: Lexical scope refers to the way variables are resolved in a programming language. It is the ability of a programming language to determine the value of a variable based on where it is defined within the source code, rather than where it is used.
Local scope: Local scope refers to the region within a function where variables declared inside the function are accessible. Variables in local scope are not accessible outside of that function.
Local Scope: Local scope refers to the accessibility and visibility of variables within a specific, confined area of a program. It determines where a variable can be accessed and modified within the code.
Module Scope: Module scope refers to the visibility and accessibility of variables, functions, and other entities within a Python module. It determines the level at which these elements can be accessed and used throughout the code, providing a way to organize and encapsulate functionality.
Namespace: A namespace is a way to organize and manage the naming of variables, functions, and other identifiers in a programming language. It provides a way to group related elements together and ensure that their names are unique within the program, preventing naming conflicts.
Nonlocal: Nonlocal is a keyword in Python that allows a function to access and modify variables from the enclosing scope, even if they are not defined within the function itself. It provides a way to work with variables that are not locally scoped to the function, enabling functions to interact with and manipulate variables from the broader context of the program.
Scope: Scope defines the region in a program where a variable is accessible. It determines the visibility and lifetime of variables.
Scope Resolution: Scope resolution is a concept in programming that determines the accessibility and visibility of variables within different parts of a program's code. It establishes the rules for how variables can be accessed and referenced, particularly in the context of nested scopes or hierarchical structures.
Variable Lifetime: Variable lifetime refers to the duration for which a variable exists and can be accessed within a program. It is closely related to the concept of variable scope, which determines the visibility and accessibility of a variable within different parts of the code.
Variable Shadowing: Variable shadowing occurs when a variable declared within a certain scope has the same name as a variable in an outer scope. This results in the inner variable 'shadowing' or hiding the outer variable within its own scope.