Scope of Variables in Python

Scope is a visibility which determines whether the variable is accessed by other parts of a code or not. Let’s see an example:

num = 5
def func(x):
    num=3
    return num
print(num)
print(func(num))
Output:
5
3

So, both print statements are printing the different results. This is what we call as Scope. Python has set of rules with which it decides what variables you are referencing in the code.

Scope can be described by LEGB rule:

1. Local
2. Enclosing funcrions
3. Global
4. Built-in

Examples of LEGB:

1. Global variables:

Global variable is declared outside of the function or in global scope. When we define a variable outside of a function, it’s global by default. Global variable can be accessed inside function also.

# num is global here
num = 5
def func():
    print(num)
print(num)
func()
Output:
5
5

Let’s see one more example:

num = 5
def func():
    num += 2
    print(num)
print(num)
func()
Output:
5
Traceback (most recent call last):
  File "/home/main.py", line 15, in <module>
    func()
  File "/home/main.py", line 11, in func
    num += 2
UnboundLocalError: local variable 'num' referenced before assignment

We are trying to change variable inside a function which is global. But, variables inside function are local by default and that’s why we got error here. We have to use global keyword to read and write a global variable inside a function.This can be solved by making the variable global explicitly as follows:

num = 5
def func():
    global num  # making variable global explicitly
    num+=2
    print(num)
print(num)
func()
Output:
5
7

• Local Variables

When we create a variable inside a function, it’s local by default.

def func():
    number =10
    print(number)
func()
Output:
10

What if we try to access variable number outside a function ?

def func():
    number =10
    print(number)
func()
print(number)
Output:
10
Traceback (most recent call last):
  File "/home/main.py", line 16, in <module>
    print(number)
NameError: name 'number' is not defined

We are trying to print local variable ‘number’ in a global scope and hence we got error.

What if we use global variable and local variable name same?

num = 5
def func():
    num=3
    print(num)
print(num)
func()
Output:
5
3

When we print the variable inside the func(), it outputs 3, i.e. local scope of variable.

Similarly, when we print the variable outside the fun(), it output 5, i.e. global scope of variable.

• Enclosing Functions

When we have function inside a function, this case may arise.

number = 5
def func():
    # Enclosing function
    number=10
    
    def func1():
        print(number)
    
    func1()
func()
Output:
10

10 is printed because func1() is enclosed inside func().

• Built in variables

Built-in means already defined in Python. Don’t assign these to another variable and don’t override these variables.

example, len is a built-in variable in Python.

print(len)
Output:
<built-in function len>

That’s it!

Happy Coding!