What is the difference between a local variable and a global variable in Python?Ava W
In Python, local variables and global variables are used to store and access data, but they differ in their scope and accessibility. Here's a detailed explanation of the differences between local and global variables: Local Variables: A local variable is a variable that is declared and defined within a specific function or block of code. It has a limited scope, meaning it is accessible only within the function or block where it is defined. Local variables are created when the function or block is entered and destroyed when it is exited.
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def my_function(): name = "Alice" print(name) my_function() # Output: "Alice" print(name) # Raises NameError: name 'name' is not defined
In this example, the variable
name is a local variable within the
my_function() function. It is defined and accessible only within the function. Trying to access the
name variable outside of the function raises a
NameError because it is out of scope.
Local variables are useful for encapsulating data within a specific function or block, preventing unintended changes or conflicts with other variables in different parts of the program.
A global variable is a variable that is declared and defined outside of any function or block. It has a global scope, meaning it is accessible from anywhere within the program, including inside functions. Global variables retain their values until they are explicitly changed or the program terminates.
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name = "Alice" def my_function(): print(name) my_function() # Output: "Alice" print(name) # Output: "Alice"
In this example, the variable
name is a global variable as it is defined outside of any function. It can be accessed both inside and outside the function
Global variables are useful when you need to share data across multiple functions or blocks within a program. However, using global variables excessively can lead to code that is difficult to maintain and debug.
Accessing Global Variables within Functions:
If a function needs to access a global variable, you can use the
global keyword to indicate that the variable being used is a global variable and not a local variable with the same name.
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name = "Alice" def my_function(): global name name = "Bob" print(name) my_function() # Output: "Bob" print(name) # Output: "Bob"
In this example, the
global keyword is used within the
my_function() function to indicate that the
name variable being modified is the global variable. Without the
global keyword, a new local variable would be created with the same name, and the global variable would remain unchanged.
To write clean and maintainable code, it is generally recommended to minimize the use of global variables and instead rely on passing values between functions or using return values. This promotes encapsulation and reduces the risk of variable name conflicts and unintended changes.
If you do need to use global variables, it's important to define them in a clear and consistent manner, ensuring they are well-documented and their usage is controlled and limited to where it is necessary.
Understanding the differences between local and global variables is crucial for writing reliable and efficient Python code, and choosing the appropriate type of variable depends on the specific needs and scope of the program.