A global variable is a variable that is declared outside of any function and can be accessed and modified throughout the entire program. You can use the global keyword to modify a global variable inside a function.
Understanding Local vs. Global Variables
Variables in Python have a scope, which defines where they can be accessed. A local variable is one that is defined inside a function and is only accessible within that function. In contrast, a global variable is defined outside any function and can be accessed anywhere in the code.
Python
x = "global" # Global variable
def my_function():
y = "local" # Local variable
print(y) # Output: local
my_function()
print(x) # Output: global
print(y) # Error: NameError: name "y" is not defined
In the above example, the variable y is local to my_function and cannot be accessed outside of it, while x is a global variable accessible from anywhere in the program.
Example of Modifying a Global Variable
Python
x = "global"
def my_function():
global x
x = "modified global"
print(x)
my_function() # Output: modified global
print(x) # Output: modified global
Without the global keyword, a variable inside a function is local and only accessible within that function. The global keyword allows you to modify the global variable within a function.
Using Global Variables Carefully
While global variables can be useful, they should be used sparingly. Overusing global variables can make your code harder to understand and debug. Here are a few best practices:
Avoid Naming Conflicts: Be careful not to use the same name for a global variable and a local variable within the same program, as this can lead to unexpected behavior.
Minimize Usage: Try to limit the use of global variables. Instead, pass variables as arguments to functions when possible.
Document Usage: Clearly comment your code when using global variables to avoid confusion for anyone reading your code.
When to Use Global Variables
There are specific scenarios where global variables are particularly useful:
Configuration Settings: Use global variables for configuration settings that need to be accessed by multiple functions or modules.
State Management: Global variables can manage the state in a program, especially in small scripts or simple applications.
Singletons: Global variables can implement singletons, where a single instance of a variable or object is shared across different parts of a program.
Global Variables
Global variable ek aisi variable hoti hai jo kisi bhi function ke bahar declare ki gayi hoti hai aur poore program mein access aur modify ki ja sakti hai. Agar aapko ek global variable ko function ke andar modify karna hai, toh aap global keyword ka use kar sakte ho.
Local vs. Global Variables Samajhna
Python mein variables ka ek scope hota hai, jo define karta hai ki unhe kahaan access kiya ja sakta hai. Ek local variable wo hoti hai jo function ke andar define hoti hai aur sirf us function ke andar hi accessible hoti hai. Iske contrast mein, ek global variable function ke bahar define hoti hai aur code ke kisi bhi part se access ki ja sakti hai.
Python
x = "global" # Global variable
def my_function():
y = "local" # Local variable
print(y) # Output: local
my_function()
print(x) # Output: global
print(y) # Error: NameError: name "y" is not defined
Is example mein, y ek local variable hai jo my_function ke andar hi accessible hai, jabki x ek global variable hai jo poore program mein kahin se bhi accessible hai.
Global Variable Modify Karne Ka Example
Python
x = "global"
def my_function():
global x
x = "modified global"
print(x)
my_function() # Output: modified global
print(x) # Output: modified global
Agar aap global keyword ka use nahi karte, toh function ke andar ki variable local hoti hai aur sirf us function ke andar hi accessible hoti hai. global keyword ka use karke aap function ke andar global variable ko modify kar sakte ho.
Global Variables Ka Dhyan Se Use Karein
Global variables useful ho sakti hain, lekin inka overuse nahi karna chahiye. Global variables ka zyada use aapke code ko samajhne aur debug karne mein mushkil bana sakta hai. Kuch best practices yeh hain:
Naming Conflicts Se Bachen: Dhyan rakhein ki aap ek hi naam ka global aur local variable ek hi program mein na use karein, kyunki isse unexpected behavior ho sakta hai.
Usage Ko Minimize Karein: Global variables ka use limit karein. Jab possible ho, variables ko functions mein arguments ke roop mein pass karein.
Usage Ko Document Karein: Apne code mein clearly comments dalen jab aap global variables ka use karein, taaki code padhne wale ko confusion na ho.
Global Variables Kab Use Karein
Kuch specific scenarios hote hain jahan global variables ka use khas faydemand hota hai:
Configuration Settings: Global variables ka use configuration settings ke liye karein jo multiple functions ya modules ke liye accessible honi chahiyein.
State Management: Global variables program mein state ko manage karne ke liye useful hoti hain, especially chote scripts ya simple applications mein.
Singletons: Global variables ka use singletons implement karne ke liye ho sakta hai, jahan ek hi instance kisi variable ya object ka program ke different parts mein share kiya jata hai.
Import Links
Here are some useful import links for further reading: