Local and Global Variables in Python

Variables that are created outside of the function are local variables and global variables are those which are defined inside a function and its scope limited to that function only means local variables are accessible only inside the function. it cannot be accessed anywhere outside the function. for global variables, parameter passing is not necessary and for local variables passing a parameter is necessary.

Global Variable

As we earlier discussed the global variable, which is created outside of a function, it is a variable that is accessible from any part of a program, as opposed to a local variable which is only accessible within the scope or block of code in which it is defined. In some programming languages, global variables are defined outside of any function or class and can be accessed and modified by any part of the program. However, the use of global variables can lead to issues with maintainability and can make code more difficult to understand and debug.

A global variable in Python is a variable that is defined outside of a function or class and can be accessed from anywhere within the program. Global variables are defined using the "global" keyword and are typically used to store information that needs to be shared across different parts of the program. However, it is generally considered best practice to avoid using global variables as they can make code more difficult to understand and maintain.

Example of Global Variable:

In this example, we will create a global variable(outside the function scope ).

Code Implementation:

x = 10

def func1():
    print(x)

def func2():
    print(x)

func1() # prints 10
func2() # prints 10

Output:

10
10

Explanation:
In the above python program we have created a variable x and assigned the value 10, and this variable can be accessible in both functions func1 and func2 because this is a global variable

Local Variable

A local variable is a variable that is only accessible within the scope or block of code in which it is defined. Local variables are typically defined within a function or a block of code and are not accessible outside of that scope. They are only visible to the code that is executing within the same scope. Using local variables can make code more modular, maintainable, and easier to understand, as the scope of the variable is clearly defined and the variable’s value is not subject to change from other parts of the program. In some programming languages, if a local variable and a global variable have the same name, the local variable will take precedence within its scope.

In Python, a local variable is a variable that is defined within a function or a block of code and is only accessible within that scope. Local variables are defined using the assignment operator (=) and are typically only used within the function or block of code in which they are defined.

Example of Local Variable:

In this example, we will create a local variable(outside the function scope ).

Code Implementation:

def func1():
    x = 20
    print(x)

def func2():
    print(x) # this will raise an error because x is not defined in this function

func1() # prints 20
func2() # raises an error

Output:

20
Traceback (most recent call last):
  File "./prog.py", line 9, in 
  File "./prog.py", line 6, in func2
NameError: name 'x' is not defined

Explanation:
In above python program we created two functions func1 and func2 and a variable x in function 1, so the print statement in func1 run properly and print 20 in output screen but print statements in func2 gives an error (name ‘x’ not defined).
We can solve this problem by taking x as a global variable. By global keyword.

Code Implementation:

# your code goes here

def func1():
    global x
    x=20
    print(x)

def func2():
    print(x) # this will raise an error because x is not defined in this function

func1() # prints 20
func2() # raises an error

Output:

20
20

Explanation:
Now here we observe that the print statement of func2 run properly did not give an error
Because of the global keyword (the keyword "global" is used to indicate that a variable is a global variable, as opposed to a local variable. This means that the variable can be accessed and modified from anywhere in the code, rather than just within the scope of the function or block in which it is defined.)so on output, we have 20 and 20.

Difference between Local Variable and Global Variable

• Scope: Global variables have a global scope and can be accessed and modified from anywhere in the code. Local variables, on the other hand, have a local scope and can only be accessed and modified within the scope of the function or class they are defined.
• Lifetime: Global variables are created when the program starts and are destroyed when the program ends. Local variables, on the other hand, are created when the function or class they are defined in is called and are destroyed when the function or class exits.
• Name collision: Global variables can have the same name as local variables and can cause confusion. To avoid this, it is recommended to use unique names for global and local variables.

Advantages and Disadvantages of Local and Global Variables

Advantages of Global Variables:

• Easy to access: Global variables can be accessed from anywhere in the code, making them easy to use.
• Shared data: Global variables can be used to share data between different functions or classes.
• Persistent data: Global variables can be used to store data that needs to persist throughout the lifetime of the program.

Disadvantages of Global Variables:

• Name collision: As mentioned earlier, global variables can have the same name as local variables, which can cause confusion.
• Side effects: Global variables can have side effects on the code when they are modified. For example, modifying a global variable in one function may cause unexpected behavior in another function that uses the same variable.
• Security: Global variables can be accessed and modified by anyone with access to the code, making them a security risk.

Advantages of Local Variables:

• Improved readability: Local variables are only visible within the scope of the function or code block in which they are defined. This makes the code more readable and easier to understand, as developers can tell exactly where and when a variable is being used.
• Reduced naming conflicts: Local variables are only accessible within the scope in which they are defined, which helps to reduce naming conflicts. This is especially important in large projects where multiple developers may be working on different parts of the codebase.
• Increased security: Local variables are not accessible from outside the scope in which they are defined, making it more difficult for malicious actors to access sensitive data. This added security can help protect against data breaches and other security threats.
• Simplified debugging: When a bug occurs, it can be easier to track down the cause if the variables are limited in scope. If a variable is only accessible within a specific function, it can narrow down the search for the problem to that specific function.

Disadvantages of Local Variables:

• Limited scope: The main disadvantage of local variables is that they are only accessible within the scope in which they are defined. This can make it difficult to share data between different functions or code blocks.
• Increased memory usage: Local variables are only stored in memory while the function or code block in which they are defined is running. This can lead to increased memory usage, especially if a large number of local variables are defined in a single function or code block.
• Extra effort: Local variables need to be defined within the function or code block in which they are being used, which can add extra effort and complexity to the development process.

Summary
Local and Global Variables are two types of variables that are used in Python programming language. A global variable is a variable that is defined outside of any function and can be accessed from anywhere in the code. On the other hand, a local variable is a variable that is defined within a function and can only be accessed within that function.

The main difference between global and local variables is their scope. Global variables have a global scope, meaning they can be accessed from anywhere in the code, while local variables have a local scope, meaning they can only be accessed within the function they were defined in.

The choice between using global and local variables in Python programming depends on the specific use case and the goals of the program. It is important to understand the differences between the two types of variables and the advantages and disadvantages of each in order to make an informed decision.