In Python, any written function can be called by another function. Note that this could be the most elegant way of breaking a problem into chunks of small problems. In this article, we will learn how can we call a defined function from another function with help of multiple examples. 

Calling and Called Function ? 
The Function which calls another Function is called Calling Function and function which is called by another Function is call Called Function.

How does Function execution work? 

A stack data structure is used during the execution of the function calls. Whenever a function is invoked then the calling function is pushed into the stack and called function is executed. When the called function completes its execution and returns then the calling function is popped from the stack and executed. Calling Function execution will be completed only when called Function is execution completes.

In the below figure. The function call is made from the Main function to Function1, Now the state of the Main function is stored in Stack, and execution of the Main function is continued when the Function 1 returns. The Fucntion1 Calls Function2 now the State of the Function1 is stored stack and execution of Function 1 will be continued when Function 2 returns. 

Consider the below Example of the function call. The Function SumOfSquares function calls the Function Square which returns the square of the number. 

# Python code to demonstrate calling the
# function from another function

def Square(X):
	# computes the Square of the given number
	# and return to the caller function
	return (X * X)

def SumofSquares(Array, n):

	# Initialize variable Sum to 0. It stores the
	# Total sum of squares of the array of elements
	Sum = 0
	for i in range(n):

		# Square of Array[i] element is stored in SquaredValue
		SquaredValue = Square(Array[i])

		# Cumulative sum is stored in Sum variable
		Sum += SquaredValue
	return Sum

# Driver Function
Array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
n = len(Array)

# Return value from the function
# Sum of Squares is stored in Total
Total = SumofSquares(Array, n)
print("Sum of the Square of List of Numbers:", Total)

Output : 

Sum of the Square of List of Numbers: 385 

Calling Function From another Function within Same class –
In the below example, the class method Function1 calls method Function2 from the class.

'''
Call a function from within another function
in the same class in Python
'''

class Main:

	# constructor of Main class
	def __init__(self):
		# Initialization of the Strings
		self.String1 ="Hello"
		self.String2 ="World"

	def Function1(self):
		# calling Function2 Method
		self.Function2()
		print("Function1 : ", self.String2)
		return

	def Function2(self):
		print("Function2 : ", self.String1)
		return

# Instance of Class Main
Object = Main()

# Calling Function1
Object.Function1()

Output :

Function2 :  Hello
Function1 :  World

Calling parent class Function from Child class Function –
Consider the below example the child class method invokes the parent class method. The child class inherits the attributes from the parent class.

# Python code to demonstrate calling parent class
# method from the child class method

class Parent:

	# constructor of Parent class
	def __init__(self):
		# Initialization of the Strings
		self.String1 ="Hello"
		self.String2 ="World"

	def Function2(self):
		print("Function2 : ", self.String1)
		return

# Child class is inheriting from Parent class
class Child(Parent):

	def Function1(self):
		# calling Function2 Method in parent class
		self.Function2()
		print("Function1 : ", self.String2)
		return

### Instance of Parent class
Object1 = Parent()

### Instance of Child class
Object2 = Child()

# Calling Function1 using Child class instance
Object2.Function1()

Output : 

Function2 :  Hello
Function1 :  World