Global and Local Variables in Python

Global and local variables in python are the two types of variables in python.

A variable that is declared inside a function or a block of code and can only be accessed inside that function or block is known as a local variable. In contrast, a global variable is one that is defined outside of a function or block and is accessible throughout the entire program.

Data values are stored in variables in Python so they can be accessed and changed at any time. In essence, a variable is a named storage location with a value in the computer’s memory.

The scope of local and global variables is the primary distinction. In contrast to global variables, which can be accessed from anywhere in the program, local variables are only accessible within the function or block in which they are defined. This indicates that whereas global variables have a wider scope, local variables have a more constrained one.

When temporary data needs to be stored within a function or block of code, local variables are used. They are helpful for storing information that will only be needed temporarily and won’t need to be accessed outside of the function or block. On the other hand, global variables are helpful for storing information that must be accessed and changed throughout the program.

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Declaring and Assigning Local Variables

Local variables are those that are declared and assigned inside of a function or code block. A local variable’s range is constrained to the function or block in which it is defined. In Python, you simply give a variable name a value inside a function or block to declare a local variable. 

For example, let’s say we want to create a function that calculates the area of a rectangle. We can declare and assign local variables for the length and width of the rectangle within the function as follows:

1def calculate_area(): length = 10 width = 5 area = length * width print("The area of the rectangle is:", area)

In this example, the variables length and width are declared and assigned within the calculate_area() function. These variables are local to the function and cannot be accessed outside of it. The variable area is also a local variable, but it is calculated based on the values of length and width.

To use the calculate_area() function, we simply call it as follows:

1calculate_area()
2The area of the rectangle is: 50

In conclusion, local and global variables are important concepts in Python programming. Local variables are used to store temporary data within a function or block of code, while global variables are used to store data that needs to be accessed and manipulated throughout the program. Understanding the difference between these two types of variables is crucial for writing efficient and effective Python programs.

Declaring and Assigning Global Variables

Global variables can be accessed from anywhere in the program and are defined outside of a function or block of code. A global variable can be accessed from anywhere in the program, including within functions or blocks of code, because its scope is wider than that of a local variable.

To declare and assign a global variable in Python, you use the global keyword followed by the variable name. This tells Python that you want to create a global variable rather than a local variable.

For example, let’s say we want to create a global variable called name that we can access from anywhere in the program. We can do this as follows:

1def print_name(): global name name = "John" print("My name is", name) print_name() print("My name is also", name) 
2# Output
3My name is John My name is also John

In this example, the global keyword is used to declare the variable name as a global variable within the print_name() function. The variable name is then assigned the value “John” within the function. After calling the function, we can also access the global variable name outside the function and print its value.

Differences Between Local and Global Variables

The scope of local and global variables is the primary distinction. In contrast to global variables, which can be accessed from anywhere in the program, local variables are only accessible within the function or block in which they are defined. Another distinction is that although local and global variables may share the same name, they are distinct variables with different values.

For example, let’s say we have a global variable called x and we also define a local variable called x within a function. The local variable x will be a different variable with a different value than the global variable x.

1x = 10 def my_function(): x = 5 print("Local x:", x) my_function() print("Global x:", x) 
2# Output 
3Local x: 5 Global x: 10

In this example, the global variable x is assigned the value 10. Within the my_function() function, we define a local variable also called x and assign it the value 5. When we call the function, it will output the value of the local variable x, which is 5. However, outside the function, the value of the global variable x is still 10.

Modifying Local and Global Variables

In Python, variables can have their values changed at the local and global levels. When a local variable is changed, only the function or block of code where the variable is defined is affected by the new value. When a global variable is changed, all of the program’s instances where it is used are affected by the new value.

For example, let’s say we have a global variable called count that we want to increment within a function. We can do this as follows:

1count = 0 def increment_count(): global count count += 1 increment_count() print(count)
2#Output
31

In this example, the increment_count() function uses the global keyword to access the global variable count. Within the function, the value of count is incremented by 1. After calling the function, we print the value of count and it will output 1.

Best Practices for Using Local and Global Variables

To write clear and effective code when using local and global variables in Python, it’s important to adhere to some best practices.

One suggestion is to use global variables as little as possible. Because changes to global variables can alter the behavior of the entire program, global variables can make code challenging to comprehend and debug. Instead, use local variables within functions or blocks of code as much as possible, as they have a smaller scope and are easier to manage.

Another suggestion is to give variables meaningful names. When working on complex programs with lots of variables, this makes the code more readable and understandable. Avoid using the same variable name for local and global variables as this can cause misunderstandings and mistakes.

When using local and global variables, common mistakes to avoid include accidentally redefining a global variable inside of a function or block of code, using global variables excessively, and failing to initialize variables correctly before using them.

Here is an illustration of how to use local and global variables in Python effectively:

1def calculate_area(length, width): # Use local variables instead of global variables area = length * width print("The area of the rectangle is:", area) length = 10 width = 5 calculate_area(length, width)

1# Give meaningful names to variables num_students = 25 # Avoid using the same variable name for local and global variables def print_name(): name = "John" print("My name is", name) print_name()

1/Code start/  # Properly initialize variables before using them total = 0 for i in range(1, 11): total += i print("The total is:", total)

In this example, we use local variables within the calculate_area() function, give meaningful names to variables, avoid using the same variable name for local and global variables, and properly initialize variables before using them. Following these best practices can help you write cleaner and more efficient code in Python.

Conclusion

Finally, it should be noted that local and global variables are crucial ideas in Python programming. Global variables are used to store data that needs to be accessed and changed across the entire program, whereas local variables are used to store temporary data within a function or block of code. The ability to distinguish between these two categories of variables is essential for creating Python programs that are both effective and efficient.

It is advised to avoid using the same variable name for local and global variables, give variables meaningful names, avoid using the same variable name for local and global variables, and properly initialize variables before using them if you want to use local and global variables effectively. Additionally, it is important to avoid common mistakes such as accidentally redefining global variables, using global variables unnecessarily, and not properly initializing variables.

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