1st PUC Computer Science Chapter 7 Functions Notes | Class 11

7.1 Introduction

The textbook introduces functions through the example of a company that manufactures tents. The tent has a cylindrical part with a conical top. To determine the selling price, the program needs to:

1. Accept the height, radius and slant height.
2. Calculate the area of canvas required.
3. Calculate the cost of the canvas.
4. Calculate the net payable amount including 18% tax.

Original Program Idea Without Functions

The textbook first demonstrates the complete calculation in one continuous program. The important calculations are:

# Calculate conical and cylindrical canvas areas
csa_conical = 3.14 * r * l
csa_cylindrical = 2 * 3.14 * r * h

canvas_area = csa_conical + csa_cylindrical

total_cost = unit_price * canvas_area
tax = 0.18 * total_cost
net_price = total_cost + tax

7.2 Functions

After defining a function, it can be called repeatedly from different parts of a program. A function can also be called from another function. Required values can be supplied through parameters.

Function-based approach

def cylindrical_area(h, r):
    return 2 * 3.14 * r * h

def conical_area(l, r):
    return 3.14 * r * l

def post_tax_price(cost):
    tax = 0.18 * cost
    return cost + tax

csa_cyl = cylindrical_area(h, r)
csa_con = conical_area(l, r)
canvas_area = csa_cyl + csa_con
total_cost = unit_price * canvas_area
net_price = post_tax_price(total_cost)

7.2.1 Advantages of Functions

7.3 User Defined Functions

Python already provides many functions through its standard library. In addition to these, programmers can create their own functions.

7.3.1 Creating User Defined Function

A user defined function definition begins with def.

def function_name([parameters]):
    statements

Important Rules

• def is used to begin a function definition.
• Parameters enclosed in brackets are optional.
• A function may have parameters or may have no parameters.
• A function may return a value or may not return a value.
• The function header ends with a colon :.
• The function name should be unique and follow identifier naming rules.
• Statements belonging to the function must be properly indented.
• Statements outside the function indentation are not considered part of the function.

Function Definition and Function Call

def add_numbers():
    first = int(input("Enter first number: "))
    second = int(input("Enter second number: "))
    total = first + second
    print("The sum is", total)

add_numbers()

7.3.2 Arguments and Parameters

def sum_n(n):
    total = 0
    for i in range(1, n + 1):
        total = total + i
    print("Sum =", total)

num = int(input("Enter n: "))
sum_n(num)

Identity of Argument and Parameter

The chapter demonstrates that before an increment operation, the argument and parameter can refer to the same value. After assigning a new value to the parameter, its identity changes.

def increase_value(num):
    print("Before:", num, id(num))
    num = num + 5
    print("After:", num, id(num))

number = int(input("Enter a number: "))
print("Argument id:", id(number))
increase_value(number)

List as an Argument

def calculate_mean(values):
    total = 0
    count = 0
    for value in values:
        total = total + value
        count = count + 1
    mean = total / count
    print("The calculated mean is:", mean)

myList = [1.3, 2.4, 3.5, 6.9]
calculate_mean(myList)

Factorial Using an Argument

def factorial_value(num):
    fact = 1
    for i in range(num, 0, -1):
        fact = fact * i
    print("Factorial of", num, "is", fact)

num = int(input("Enter the number: "))
factorial_value(num)

String as Parameters

Arguments passed to a function need not always be numeric. String values can also be passed as arguments. The chapter demonstrates joining first name and last name to form a full name.

def full_name(first, last):
    name = first + " " + last
    print("Hello", name)

first = input("Enter first name: ")
last = input("Enter last name: ")
full_name(first, last)

Default Parameter

def mixed_fraction(num, deno=1):
    remainder = num % deno

    if remainder != 0:
        quotient = int(num / deno)
        print("Mixed fraction =", quotient, "(", remainder, "/", deno, ")")
    else:
        print("The fraction evaluates to a whole number")

For example, if the function is called as mixed_fraction(9), the parameter num receives 9 and deno uses its default value 1. If a denominator is supplied, the supplied value replaces the default.

Important Rules for Default Parameters

• Arguments should correspond to parameters in the same order.
• An argument may also be an expression.
• Default parameters must be trailing parameters.
• If a parameter has a default value, parameters to its right must also have default values.

7.3.3 Functions Returning Value

A function may or may not return a value. Functions that perform calculations and only display results without returning a value are described in the chapter as void functions.

Function with Return Value

def calculate_power(number, power):
    result = 1

    for i in range(1, power + 1):
        result = result * number

    return result

base = int(input("Enter the Base: "))
expo = int(input("Enter the Exponent: "))

answer = calculate_power(base, expo)

print(base, "raised to the power", expo, "is", answer)

Four Function Forms

Returning Multiple Values

A function can return multiple values through a tuple. The chapter demonstrates returning the area and perimeter of a rectangle.

def rectangle_values(length, breadth):
    area = length * breadth
    perimeter = 2 * (length + breadth)
    return (area, perimeter)

l = float(input("Enter length: "))
b = float(input("Enter breadth: "))

area, perimeter = rectangle_values(l, b)

print("Area is:", area)
print("Perimeter is:", perimeter)

7.3.4 Flow of Execution

The Python interpreter starts from the first statement and normally executes statements from top to bottom. However, when it encounters a function definition, the statements inside that function are not executed until the function is called. When a function call is reached, control moves to the called function, executes it, and then returns to the point of the call.

# Correct order
def helloPython():
    print("I love Programming")

helloPython()

Order of Execution Illustration

def Greetings(Name):
    print("Hello " + Name)

Greetings("John")
print("Thanks")

def RectangleArea(l,b):
    return l*b

l = input("Length: ")
b = input("Breadth: ")

Area = RectangleArea(l,b)
print(Area)
print("thanks")

7.4 Scope of a Variable

The chapter describes two scopes:

Global Variable

Local Variable

Example of Global and Local Variables

num = 5

def my_function():
    local_value = num + 5
    print("Global value:", num)
    print("Local value:", local_value)

my_function()

print("Global outside:", num)

Using the global Keyword

If a function needs to modify a global variable and use the modified value outside the function, the keyword global is used before the variable name inside the function.

num = 5

def update_number():
    global num
    print("Accessing num =", num)
    num = 10
    print("num reassigned =", num)

update_number()
print("Accessing num outside function =", num)

7.5 Python Standard Library

7.5.1 Built-in Functions

Examples used in the chapter include input(), int() and print().

fname = input("Enter your name: ")

Here, input() receives an argument and returns a value which is stored in fname.

Categories of Built-in Functions

Common Built-in Functions

7.5.2 Module

A function is a grouping of instructions, while a module is a grouping of functions. A module is created as a Python .py file.

Importing a Module

import modulename

Multiple modules can be imported using the appropriate comma-separated form.

Calling a Module Function

modulename.functionname()

The function name is preceded by the module name and a dot.

Built-in Module: math

The math module contains different mathematical functions. Many functions in this module return floating-point values.

import math

Built-in Module: random

The random module contains functions used to generate random numbers.

import random

Built-in Module: statistics

The statistics module provides functions for calculating statistics of numeric, real-valued data.

import statistics

From Statement

Instead of importing an entire module, the from statement can be used to access only the required function or functions.

from modulename import functionname

from modulename import function1, function2

When a function is imported using the from statement, the module name does not need to be written before the function call.

from random import random

print(random())

from math import ceil, sqrt

value = ceil(624.7)
print(sqrt(value))

Composition

from math import ceil, sqrt

value = ceil(624.7)
answer = sqrt(value)

print(answer)

The same dependency can also be written as:

sqrt(ceil(624.7))

Other composition examples from the chapter include expressions involving input(), int(), mathematical functions and arithmetic expressions.

Docstrings

User Defined Module: basic_math

"""
basic_math Module
*****************
This module contains basic arithmetic operations
that can be carried out on numbers
"""

def addnum(x, y):
    return x + y

def subnum(x, y):
    return x - y

def multnum(x, y):
    return x * y

def divnum(x, y):
    if y == 0:
        print("Division by Zero Error")
    else:
        return x / y

Using the Module

import basic_math

print(basic_math.__doc__)

a = basic_math.addnum(2,5)
print(a)

a = basic_math.subnum(2,5)
print(a)

a = basic_math.multnum(2,5)
print(a)

a = basic_math.divnum(2,5)
print(a)

a = basic_math.divnum(2,0)

Application Example: Traffic Light Functions

The chapter also demonstrates a program in which one user defined function calls another function. The traffic-light colour is checked and another function returns a value representing the colour.

def traffic_light():
    signal = input("Enter the colour of the traffic light: ")

    if signal not in ("RED", "YELLOW", "GREEN"):
        print("Please enter a valid Traffic Light colour in CAPITALS")
    else:
        value = light(signal)

        if value == 0:
            print("STOP, Your Life is Precious.")
        elif value == 1:
            print("PLEASE GO SLOW.")
        else:
            print("GO!, Thank you for being patient.")

def light(colour):
    if colour == "RED":
        return 0
    elif colour == "YELLOW":
        return 1
    else:
        return 2

traffic_light()
print("SPEED THRILLS BUT KILLS")

⚡ Quick Revision

def name():
    statements

def name(parameter):
    statements

return value

import module

module.function()

from module import function

High-Value Exam Points

• Functions provide modularity and reusability.
• A user defined function begins with def.
• Function header ends with a colon.
• Arguments are values passed during a function call.
• Parameters receive the corresponding arguments.
• Default parameters have pre-decided values.
• Default parameters must be trailing parameters.
• return transfers control back to the calling function and can return a value.
• Multiple values can be returned using a tuple.
• A function definition should appear before its call in the program.
• Global variables are defined outside a particular function.
• Local variables are defined inside a function or block.
• The global keyword is used when a function needs to modify the global variable.
• Built-in functions are ready-made functions available in Python.
• A module is a Python file containing function definitions.
• import makes module functions available.
• from can be used to import only required functions.
• Python is case sensitive.
• Only required functions can be imported to save memory.

Important Built-in Functions

📝 Important Questions & Answers

Difference Questions

Chapter Exercise & Exam Practice

The following questions are based on the exercise, activity-based questions, suggested lab exercises and case-study section of the uploaded chapter.

Error Identification

1. Identify the error in a function definition where the function expects two parameters but only one value is passed.
2. Identify the problem when a function uses a function name that has not been imported.
3. Identify the error caused by trying to modify a variable inside a function without correctly handling its global scope.
4. Identify the error in a function header where a non-default parameter follows a default parameter.
5. Identify the error in an invalid assignment involving a function call and returned value.

Conceptual Practice

1. How is math.ceil(89.7) different from math.floor(89.7)?
2. Which function is suitable for generating random numbers between 1 and 5: random() or randint()? Give the reason.
3. Differentiate between built-in pow() and math.pow() with an example.
4. Show with an example how a Python function can return multiple values.
5. Differentiate between argument and parameter with an example.
6. Differentiate between global and local variables with an example.
7. Does a function always return a value? Explain.

Activity-Based / Programming Practice

1. Create a login function that accepts user ID and password and handles limited wrong attempts.
2. Create a discount program using a user defined function based on shopping amount and membership conditions.
3. Create a learning program using functions for simple words and single-digit addition.
4. Create a program to generate the Fibonacci sequence using functions.
5. Create a menu-driven calculator using functions for arithmetic operations and selected mathematical functions.

Suggested Lab Exercises

1. Write a function to check divisibility of a number by 7.
2. Write a function that accepts name and gender and prefixes an appropriate title.
3. Write a function to calculate the determinant of a quadratic equation using b² - 4ac and classify it according to the sign of the determinant.
4. Use the random module to automate a lucky draw from token IDs.
5. Write a function to calculate compound interest using the given formula and parameters.
6. Write a function that accepts two numbers, swaps them when required, and returns them.
7. Create functions for area, perimeter or surface area of shapes such as square, rectangle, triangle, circle and cylinder and use them through a module.
8. Create a five-question GK quiz with randomly displayed questions and functions for scoring and remarks.

Case Study Practice

1. Convert the functionality of earlier chapter programs into user defined functions.
2. Add a function to check short attendance by calculating attendance percentage and returning an appropriate value according to the chapter’s stated condition.