function

1. Functions
In
Python

2. Learning Objectives
● Explain how to define and write functions
● Illustrate how to call functions
● Analyze how to pass different arguments to
functions
● Demonstrate how to return a value from
functions
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3. Working Example
Write a Python Program to calculate the mean of five
numbers input by user.
Formula for calculating the mean is:
For Example:
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Input: 1, 2, 3, 4
Output: 2.5
Mean = {Sum of numbers} ÷ {Total numbers}

4. Working Example: Solution
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add = 0
for x in range(0,5,1):
num = int(input(“Enter Number: ”))
add = add + num
print(“Mean: ”, add/5)
Output:
Enter Number: 1
Enter Number: 2
Enter Number: 3
Enter Number: 4
Enter Number: 5
Mean: 3.0
To calculate the mean,
We can use this method

5. Is there any better Solution?
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add = 0
for x in range(0,5,1):
num = int(input(“Enter Number: ”))
add = add + num
print(“Mean: ”, add/5)
Output:
Enter Number: 1
Enter Number: 2
Enter Number: 3
Enter Number: 4
Enter Number: 5
Mean: 3.0
To calculate the mean,
We can use this method

6. Is there any better Solution?
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● Better solution in terms of readability and
simplicity.
● Yes, there is.
● But before moving to the solution lets take a real
life example of Automobile factory.

7. Automobiles in Factory
● How do the automobiles are created in the
factory?
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8. Components of Automobiles
● Wheels, Brakes, Engine, Steering Wheels etc are
the components of the car.
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9. Automobiles in Factory
● Wheels, Brakes, Engine, Steering Wheels are
manufactured separately and they are assembled
in the automobile factory.
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10. Functions
● Functions are like short programs that can take
input, process on it, and may return the results
● Functions are like building blocks. They let you
divide complicated programs into manageable
pieces
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11. Functions: How to Create?
● Functions are defined using “def” keyword in python.
● Parameters are inputs to the function and they are
separated by commas.
● “return” is the keyword for returning the output
● Example:
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12. Functions: How to Call?
● Functions are called by writing the name of the
function and passing the parameters to the
functions.
● Output of the function is received in a new
variable.
● Example:
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13. Functions: Previous Example
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Let’s Use Functions to solve the same problem.

14. Functions: Previous Example
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def calculate_sum():
add = 0
for x in range(0,5,1):
num = int(input("Enter Number: "))
add = add + num
return add
To calculate the sum,
We can use this
function
def calculate_avg(sum):
avg = sum/5
return avg
To calculate the average,
We can use this method
sum = calculate_sum()
print("Mean: ", calculate_avg(sum))
The rest of program
would look like this.

15. User-Defined Functions:
● These Functions are called user-defined functions
because they are defined by the users.
● For the program’s simplicity and more readability,
users can define as many functions as they want.
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16. User-Defined Functions: Benefits
● Functions make the code reusable. We can declare
them once and use them multiple times.
● Functions make the program easier as each small
task is divided into a function.
● Functions increase readability.
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17. Two-types of Functions:
● User-Defined Functions
● Pre-Defined (Library) Functions
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18. Pre-Defined (Library) Functions:
● Library functions are the built-in functions in
Python programming.
● Programmers can use library functions by invoking
the functions directly; they don't need to write
the functions themselves.
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19. Functions: Previous Example
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Instead of writing this complete code, Python library (statistics) has
already written this code.

20. Pre-Defined Functions: Extended
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import statistics
my_list = []
for x in range(0,5,1):
y = int(input("Enter Number: "))
my_list.append(y)
mean = float(statistics.mean(my_list))
print("Mean: ", mean)
Output:
Enter Number: 1
Enter Number: 2
Enter Number: 3
Enter Number: 4
Enter Number: 5
Mean: 3.0
To calculate the mean,
We can use Pre-defined Functions
Don’t Worry. We will learn
about Lists in Coming Lectures.

21. Built-in Functions: Python Standard library
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22. Built-in Functions: with importing math library
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● import maths

23. Built-in Functions: with importing math library
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● For Example:

24. Learning Objective
In this lecture, we learnt about functions,
how to define functions with different
parameters, differentiate between built-in
and user-defined functions.
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25. Conclusion
● A function is a block of organized, reusable code
that is used to perform a single, related action.
● Functions are of 2 types
○ Built-in Functions User-defined
Functions
● Functions can have zero or more parameters.
● Syntax to define and call Functions is as follows:
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26. Take Home Tasks
1. Create a function that takes the age in years and returns
the age in days.
Note:
● Use 365 days as the length of a year for this challenge.
● Ignore leap years and days between last birthday and now.
● Expect only positive integer inputs.
Examples:
● calcAge(65) ➞ 23725
● calcAge(0) ➞ 0
● calcAge(20) ➞ 7300
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