14-local-global.md

Python Local and Global Variables

Video link: https://youtu.be/ngCDTEWVjrQ

In this video, we learned about the concept of global and local variables in Python.

Programs in the Video

• Local Variables
• Global Variables

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Local Variables

A variable declared inside the function's body or in the local scope is known as a local variable.

Suppose we have the following function:

def add_numbers(n1, n2):
    result = n1 + n2
    print(result)

add_numbers(2, 5)

Let's try to print the result variable from outside the function.

def add_numbers(n1, n2):
    result = n1 + n2

add_numbers(2, 5)
print(result)

Output

Traceback (most recent call last):
  File "<string>", line 5, in <module>
NameError: name 'result' is not defined

This error is saying that the result variable is not defined in line 5.

Any variable that is created inside a function is local to it. The result variable is local to the add_numbers() function.

We can fix this by using a return statement:

def add_numbers(n1, n2):
    result = n1 + n2
    return result

output = add_numbers(2, 5)
print(output)

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Global Variables

In Python, a variable declared outside of the function or in global scope is known as a global variable.

This means that a global variable can be accessed inside or outside of the function.

For example,

message = "How you doing?"

def greet():
    print(message)

greet()

Output

How you doing?

Here, message is a global variable and can be used anywhere in the program.

Let's see what happens if a local variable with the same name is defined.

message = "How you doing?"

def greet():
    message = "How are you?"
    print("Message inside function:", message)

greet()
print("Message outside function:", message)

Output

Message inside function How are you?
Message outside function: How you doing?

Rather than changing the global message variable, a new local variable is created with the new value.

However, the global message variable is not changed, so it gets printed outside the function as it is.

---

global keyword

If we need to change the global variable inside the function, we can use the global keyword:

def greet():
    global message
    message = "How are you?"
    print("Message inside function", message)

greet()
print("Message outside function:", message)

Output

Message inside function How are you?
Message outside function: How are you?

The global variable tells Python that the variable we are referring to is the global variable.

After we change the global message variable, the changes are reflected in the global scope as well.