Python Basics 101 — Variables, Data Types & Operators

What Is Python and Why Should You Learn It?

Think about this: you want to tell your friend how to make chai. You'd say it in Malayalam or English — a language you both understand. A computer only understands its own language, called machine code — which is basically millions of zeros and ones. Writing in zeros and ones is painful. So we use programming languages like Python as a translator.

You write instructions in Python. Python translates them into machine code. The computer runs them. Simple.

Why Python specifically?

• Used in AI and Machine Learning — the same tools behind ChatGPT, image recognition, recommendation systems
• Used in automation — write a script to rename 10,000 files in seconds instead of doing it manually
• Used in web development, data science, finance, biomedical research
• Readable syntax — Python code almost reads like English sentences
• Huge community — if you get stuck, someone has already asked your question and answered it on Stack Overflow

Your very first Python instruction

The most important thing in any new language is saying "hello." In Python, print() is the function that displays something on the screen. Think of it as Python's way of speaking out loud.

print("Hello, World!")
print("My name is Python")

Run those two lines and you will see both messages appear. Every word inside the quotes is displayed exactly as written. The print() function will become your best debugging friend — whenever something goes wrong, print the value and see what Python is actually seeing.

Variables — The Labelled Boxes

Imagine you have a tiffin box. The box itself is the variable. The food inside is the value. You write your name on the box so you know which one is yours. Later you can swap the food inside — the box stays the same, only the contents change.

In Python, a variable is a labelled storage location in the computer's memory. You create one by writing a name, the = sign, and the value you want to store.

name = "Arjun"
age = 20
marks = 95.5
is_passed = True

print(name)    # Output: Arjun
print(age)     # Output: 20
print(marks)   # Output: 95.5

Now if Arjun's marks change after a revaluation, you just update the variable. Everything that uses marks automatically gets the new value — you don't have to hunt through your entire program and change it everywhere.

marks = 95.5
print(marks)    # Output: 95.5

marks = 97.0    # Revaluation result
print(marks)    # Output: 97.0 — same box, new food inside

Rules for naming variables

• No spaces — use underscore instead: student_name not student name
• Cannot start with a number — 2marks is invalid, marks2 is fine
• Case-sensitive — Name and name are two different variables
• Only letters, numbers, and underscores — no special characters like @, #, -
• Keep names meaningful — student_age is better than x

Data Types — Not All Information Is the Same

A good tiffin box has separate compartments — one for rice, one for curry, one for pickle. You would not mix them all into one compartment (well, most people wouldn't). Similarly, Python understands that different kinds of information need to be handled differently. These different kinds are called data types.

int — Whole Numbers

Short for "integer." These are counting numbers — no decimal point. Roll numbers, years, quantities, sensor readings that come as whole numbers.

float — Decimal Numbers

Short for "floating point number." These have a decimal point. Percentages, voltage readings, GPS coordinates, temperatures.

str — Text (Strings)

Short for "string." Any text goes in quotes — single or double, both work. Even if a number is inside quotes, Python treats it as text, not a number. So "42" is not the same as 42.

bool — True or False

Short for "boolean." Only two possible values: True or False (capital T and F). Like a yes/no question — "Did the student pass?" True or False. "Is the sensor triggered?" True or False.

roll_number = 42           # int
percentage = 87.5          # float
student_name = "Meera"    # str
has_submitted = True       # bool

# Check what type any variable is:
print(type(roll_number))   # <class 'int'>
print(type(percentage))    # <class 'float'>
print(type(student_name))  # <class 'str'>
print(type(has_submitted)) # <class 'bool'>

Operators — Making Python Do the Work

An operator is a symbol that tells Python to perform an operation. Just like a calculator has +, -, ×, ÷ buttons, Python has operators for math, comparisons, and combining conditions.

Arithmetic Operators

a = 17
b = 5

print(a + b)   # Addition        → 22
print(a - b)   # Subtraction     → 12
print(a * b)   # Multiplication  → 85
print(a / b)   # Division        → 3.4  (always gives float)
print(a // b)  # Floor division  → 3    (removes decimal part)
print(a % b)   # Modulus/remainder → 2  (17 = 5×3 + 2)
print(a ** b)  # Power/exponent  → 1419857  (17 to the power 5)

A Practical Example — Calculating Percentage

marks_obtained = 427
total_marks = 500

percentage = (marks_obtained / total_marks) * 100
print(percentage)   # Output: 85.4

Comparison Operators — Asking Yes/No Questions

Comparison operators always return True or False. They are the foundation of all decision-making in code.

score = 78

print(score == 78)   # Equal to?         → True
print(score != 100)  # Not equal to?     → True
print(score > 60)    # Greater than?     → True
print(score < 40)    # Less than?        → False
print(score >= 78)   # Greater or equal? → True
print(score <= 77)   # Less or equal?    → False

Logical Operators — Combining Conditions

Like combining sentences: "If it is raining AND you don't have an umbrella, take the bus." In Python, and, or, and not combine True/False values.

Your First Real Program

Theory is good. Programs are better. Let's build something that actually does something useful: a program that takes a student's marks, calculates their percentage, and tells them whether they passed or failed.

This uses everything from this page — variables, data types, arithmetic operators, and comparison operators — all in one place.

Do not worry about the if/else part yet — we cover that in detail in Python 102. For now, just notice how the variables, operators, and types all work together to make something useful.