This document discusses functions in Python. It explains how to define functions using the def keyword, how to call functions, and how to pass arguments and return values. It differentiates between user-defined functions and built-in functions from Python's standard library, giving examples using the math and statistics libraries. The document concludes that functions make code more organized and reusable.

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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