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Sabin Sim
Sabin Sim

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Python basics - Day 02

#python #developer #programming #softwareengineering

Day 2 – Variables and Data Types

Project: Build a “User Info Display App”

01. Learning Goal

By the end of this lesson, you will be able to:

  • Understand what variables are and how to use them
  • Work with Python’s basic data types (int, float, str, bool)
  • Convert between data types using casting
  • Build a simple Python app that prints user information

02. Problem Scenario

You are creating a small program that stores user details such as name, age, and height.

Your goal is to correctly assign values to variables, identify their data types, and display them on screen.

03. Step 1 – What Is a Variable?

A variable is like a label used to store data.

Use the = operator to assign values.

x = 10          # Integer (int)
y = 3.14        # Float
name = "Sabin"  # String (str)
is_ok = True    # Boolean (bool)
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04. Step 2 – Primitive Data Types

Integers (int)
Example: age = 25 → print(age, type(age)) will show 25 <class 'int'>.

Floats (float)
Example: pi = 3.14159 → print(pi, type(pi)) outputs 3.14159 <class 'float'>.

Strings (str)
Example: greeting = "Hello" → print(greeting, type(greeting)) gives Hello <class 'str'>.

Booleans (bool)
Example: is_student = True → print(is_student, type(is_student)) outputs True <class 'bool'>.

05. Step 3 – Variable Naming Rules

Follow these rules:

  • ✅ Use letters, numbers, and underscores (_)
  • ❌ Do not start with a number
  • ✅ Case-sensitive (Name ≠ name)
  • ✅ Use meaningful names

Example of good vs bad naming:

a = 10               # ❌ Not descriptive
student_age = 20     # ✅ Clear and meaningful
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06. Step 4 – Type Casting (Data Conversion)

Convert between types using built-in functions.

x = 10
print(float(x))  # int → float: 10.0

y = 3.99
print(int(y))    # float → int: 3

num_str = "100"
print(int(num_str) + 1)  # str → int: 101

age = 25
print("Age: " + str(age))  # int → str: Age: 25
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07. Step 5 – Mini Project: User Info Display App

Combine everything to display user info in one script.

name = "Sabin"
age = 30
height = 175.5
is_student = False

print("Name:", name)
print("Age:", age)
print("Height:", height)
print("Is student?", is_student)
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08. Practice Task

  1. Ask the user for their name and age using input().
  2. Convert the age to an integer and calculate next year’s age.
  3. Display the result using an f-string. 
name = input("Enter your name: ")
age = int(input("Enter your age: "))
print(f"Hi {name}! You'll be {age + 1} next year.")
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09. Reflection

You have learned to:

  • Use variables to store values
  • Work with int, float, str, and bool types
  • Convert between types using casting
  • Build a simple User Info App that prints formatted output

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