Your First Program: print, Variables and input

Every program does the same three things: it takes some data, works on it, and shows a result. On this page you will learn the smallest pieces that make that possible — print, comments, variables and input.

Printing output

print() shows whatever you put between its brackets. Text goes inside quotes; numbers and calculations do not. Give it several things separated by commas and it prints them with spaces between:

print("Python for AI")
print("Lesson", 1, "of", 20)
print(7 * 6)

Python for AI
Lesson 1 of 20
42

Comments

Anything after a # on a line is a comment: Python ignores it. Comments are notes for humans — including you, three weeks from now. Explain why the code does something, not what every line obviously does.

Variables: names for values

A variable is a name that refers to a value. You create one with =, which means "store", not "is equal to":

model_name = "gpt-5.5"      # text (a string)
max_tokens = 500            # a whole number (an integer)
temperature = 0.7           # a decimal number (a float)
is_streaming = False        # True or False (a boolean)

print(model_name, max_tokens, temperature, is_streaming)

max_tokens = max_tokens + 100   # a variable can change
print(max_tokens)

gpt-5.5 500 0.7 False
600

Notice the last two lines. max_tokens = max_tokens + 100 reads the current value (500), adds 100 and stores the result back under the same name. In maths that line would be nonsense; in programming it is everyday work.

Naming rules and style

• Names can contain letters, digits and underscores, but cannot start with a digit: model_2 is fine, 2model is not.
• Names are case-sensitive: Model and model are different variables.
• Python style (called PEP 8) uses snake_case: lower-case words joined by underscores.
• Choose names that say what the value means: temperature, not t.

Every value has a type

Python keeps track of what kind of value each one is. type() tells you:

print(type("hello"))
print(type(42))
print(type(3.14))
print(type(True))

<class 'str'>
<class 'int'>
<class 'float'>
<class 'bool'>

You will meet these four types — str, int, float and bool — properly on the next page.

Asking the user: input()

input() shows a question, waits for the user to type something and press Enter, and gives you what they typed as text:

name = input("What is your name? ")
print("Welcome to Python, " + name + "!")

If the user types Rahim:

What is your name? Rahim
Welcome to Python, Rahim!

Your first error message

Errors are normal. What matters is reading them. Here a variable name is misspelt:

greeting = "Hello"
print(greting)

Traceback (most recent call last):
  File "main.py", line 2, in <module>
    print(greting)
          ^^^^^^^
NameError: name 'greting' is not defined. Did you mean: 'greeting'?

Read error messages from the bottom up. The last line names the problem (NameError: Python does not know the name greting) and even suggests the fix. The lines above it say where: line 2. Most beginner errors are this kind — a typo, a missing quote or bracket — and are fixed in seconds once you read the message.

Try it yourself

1. Write a program that asks for the user's name and city, then prints Rahim lives in Dhaka.
2. Store the number of hours you will study each day in a variable, and print how many hours that is in 30 days.
3. Make a deliberate typo in a variable name and read the error message.