Python Programming : Basics (Leaving Cert Computer Science): Revision Notes

Python Programming : Basics

Python Overview

Python is a high-level, interpreted programming language known for its simplicity and readability.

It is a suitable language for those who are beginning to code due to its clear syntax.

The first Python programme we write will print a message to the console.

print("Hello World")

Variable & Data Types

Variables are used to store values such as integers. Think of a variable as a name attached to a particular object. To create a variable, we assign it value using the assignment operator, which is single equals (=).

n = 100  # n is assigned to the value 100
print(n) # this will print 100

n = 200 # n is now assigned to the value 200

Like most programming languages, Python supports many data types. To get the data type of a specific variable, we can use the type function.

Integers are whole positive number.

integer = 30
print(type(integer))  # <class 'int'>

Floats (short for floating-point number) are used to represent real numbers that have fractional parts, i.e. decimal numbers.

decimal_number = 3.14
print(type(integer))  # <class 'float'>

Strings are sequences of characters.

sentence = "Hello Python!"
name = 'John Doe'
print(type(name))  # <class 'str'>

Booleans are either True or False

is_authenticated = True
print(type(is_authenticated ))  # <class 'bool'>

Operations

In Python, different data types support various operations. In mathematics, it is well-known that we can add two integers. Addition is the operations and the two integers are the operands.

# arithmetic operations - applicable to ints, floats (numeric types)
a = 5
b = 3

# addition, subtraction, multiplication, division
c = a + b  # c is assigned to 8
d = a - b  # d is assigned to 2
e = a * b  # e is assigned to 15
f = a / b  # f is assigned to 1.6666666666666667

# floor division (divides, then rounds down)
g = a // b  # g is assigned to 1

# modulus (returns the remainder of division)
h = a % b  # h is assigned to 2

# exponentiation 
i = a ** b  # i is assigned to 125

Python also supports comparison operations. Arithmetic operations operate on numeric values, and return numeric values. Comparison operations operate on many types of values and return Boolean values.

# comparison operations
a = 10
b = 20 
c = 30
d = 10

# equal to 
print(a == d)  # True
print(a == b)  # False 

# not equal to 
print(a != d)  # False
print(a != b)  # True

# greater than 
print(c > d)  # True

# less than 
print(d < c) # True

# greater or equal to 
print(c >= b) # True
print(a >= d) # True

# less than or equal to
print(c <= b) # False
print(a <= d) # True

Variables in Python can be converted from data type to another. In most programming languages this is know as type casting.

number_as_string = "3"   # I want to convert "3" to 3  (string to int)
number_as_int = int(number_as_string)

b = 4 
print(number_as_int + b)  # 7

User Input

In some cases we would like to get input from the user. This is typically done using the input function.

user_input = input("Enter Something : ")
print("You entered:", user_input)

This code snippet will call the input function, which waits for the user to input something. This input is always a string, you often need to convert it to other data types if the a string is not what you want.

name = input("Enter Your name : ")
age = input("Enter your age: ")

print("Hello " + name + ", you are " + age + " years old")

Questions

Question 1

• Define two variables, length and width to store the dimensions of a rectangle. Calculate and print the area of the rectangle.

Question 2

• Create a variable text containing the string "Python Programming". Print the number of characters in text.

Question 3

• Write a programme that takes in three integers from the user and prints the average of those numbers

Question 4

• Write a programme that takes the radius and height of a cylinder from the user and print its volume. The volume of a cylinder is $πr^2h$.

import maths

pi = maths.pi

Question 5

• Write a programme that takes the user's birth year as input and calculates their age

Question 6

• Write a programme that takes the user's birth year as input and calculates their age