2. Data Types and Operations - MantsSk/CA_PTUA14 GitHub Wiki

Introduction

Python Data Types are used to define the type of a variable. It defines what type of data we are going to store in a variable. The data stored in memory can be of many types. For example, a person's age is stored as a numeric value and his or her address is stored as alphanumeric characters.

Integers

Z = {..., -3, -2, -1, 0, 1, 2, 3, ...}

How to instantiate a variable as an integer in Python

a = 5
print(a)

b = 25
print(b)

Integer Operations

Possible operations:

Operation	Result
x + y	sum of x and y
x - y	difference of x and y
x * y	product of x and y
x / y	quotient of x and y
x // y	floored quotient of x and y
x % y	remainder of x / y
x ** y	x to the power y

a = 5
b = 25

c = a + b 
print(c)

c = a - b
print(c)

c = a * b
print(c)

c = b / a
print(c)

c = b // a
print(c)


c = a % b
print(c)

c = a ** b
print(c)

Float type

Z = {..., -2.5 , ..., -2.0, ... , -1.0, ... , 0, ... , 1.0, ... , 2.0, ... , 2.5, ...}

Note that there can be endless number possibilities between two floats.

Float Operations

Same operations/ mathematical expressions apply to the float numbers

Possible operations:

Operation	Result
x + y	sum of x and y
x - y	difference of x and y
x * y	product of x and y
x / y	quotient of x and y
x // y	floored quotient of x and y
x % y	remainder of x / y
x ** y	x to the power y

a = 5.5
b = 25.3

c = a + b 
print(c)

c = a - b
print(c)

c = a * b
print(c)

c = b / a
print(a)

c = b // a
print(a)


c = a % b
print(c)

c = a ** b
print(c)

String

String is simply a piece of text, it could be a single letter or the while word or an entire sentence:

letter = "a"
name = "Code Academy"
sentence = "I really enjoy learning python !"

String operations

Strings have plenty of useful in-built functionality in Python, more information here

What is more with strings we can select certain characters from the word. In python it works:

name = "Code Academy"
print(name[5])

# A

print(name[-2])

# m

print(name[5:12])

# Academy

print(name[5:])

# Academy

print(name[:4])

# Code

print(name[5:12:1])

# Academy

print(name[5::2])

# Aaey

print(name[::-1])

# ymedacA edoC

print(name.split())

# ['Code', 'Academy']

print(name.upper())

# CODE ACADEMY

print(name.replace('c', 'k'))

# Code Akademy

print(name.replace('Code', 'Music'))

It is also possible to get the last or second to last character from string:

print(name[-1])
print(name[-2])

You can also do slicing of string:

name = "Code Academy"
print(name[:4])

print(name[5:12])

Try doing any of the methods that are described in the link above:

name = "Code Academy"
print(name.upper())

print(name.replace('c', 'k'))

Or any other as you wish.

Combining of string

You may also combine various string together to make other variables:

greeting = "Hello, my name is"
name = "Tom"

completed_greeting = f"{greeting} {name}"
print(completed_greeting)

Or:

greeting = "Hello, my name is"
name = "Tom"

completed_greeting = greeting + " " + name
print(completed_greeting)

Wow! "+" operator does work on strings too! All it does is concatenation. Such trick has a term Operator overloading we will learn some tricks how to apply what certain operators can do to our classes. Unfortunately "-" in the case of string does not make any particular sense so this method is not allowed on string type.

Conversion of types

What is more important to mention are methods allowing to transform data from one type to another:

str()
int()
float()

What is important to mention here is not all data types are compatible for such operations. For example:

a = "Hello"
b = int(a)

This will simply throw an error because it does not even make sense how the alhapnumeric value can suddenly become an integer

Rule of thumb is that all integers, floats can be translated to string, but only numeric strings can be transformed to int() or float():

✅ 
a = "55"
b = int(a)
c = float(a)

a = 55
b = str(a)
c = float(a)

🛑 
a = "Hello"
b = int(a)

c = float(a)

User input

You program may ask user to enter something and use it for the further operations:

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

print(f"Your name is {name}, you are {age} years old"

Variable naming conventions

As per PEP8 https://peps.python.org/pep-0008/ there are some guidelines to follow when naming your variables. In Python simple variables as we have seen today should be named with snake_case style. What is more constants should be all capital letter, and hidden variables or functions should start with "_".

✅

_hidden_variable = "secret"
PI = 3.14
first_name = "Albert"
last_name = "Einstein"

⛔ possible but does not comply with PEP8:

FirstName = "Albert"
First_Name = "Albert"
FIRST_NAME = "Albert"

Python will understand such notion but your colleagues will hate you for this, so please following the naming conventions to make life easy to everyone.

Variables cannot be called as Python built in functions or special words like: 'False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield'