Hello, World!

Lesson 1 of 31 · Part 1 · Basics · about 15 minutes

Your first program is one line long. It tells Python to show a message on the screen. Every example on this page runs right here in your browser: press Run, change something, run it again.

main.py

1print("Hello, World!")

Output

Hello, World!

That line is a complete Python program. Here is what each piece does:

Piece	What it is
`print`	A built-in function: a ready-made command that shows things on the screen.
`( )`	Whatever goes between the parentheses is handed to `print`. Parentheses always come in pairs.
`"Hello, World!"`	A string: a piece of text. The quotes say where the text starts and ends; they are not shown.

One line at a time

A program can be many lines long. Python runs them in order, from the top down. Press Step to watch it happen one line at a time.

main.py

1print("Wick wakes up")2print("Lamps to light:", 3)3print("Off we go!")

Output

Wick wakes up
Lamps to light: 3
Off we go!

Tip: Step works on every example in the course. Use it whenever a result surprises you.

Text needs quotes

Quotes tell Python "this is text, show it as it is". Without quotes, Python treats what it sees as code and works it out first.

Guess first

What does the second line print?

1print("7 + 3")2print(7 + 3)

The first line has quotes, so it shows the text 7 + 3. The second has none, so Python does the sum and shows 10.

Output

Single quotes work too, as long as both ends match. Pick the kind that is not inside your text:

main.py

1print('Single quotes work too')2print("It's easy with double quotes")3print('She said "hi"')

Output

Single quotes work too
It's easy with double quotes
She said "hi"

Several things on one line

Give print several values, separated by commas. It puts a space between them. Two optional settings change that: sep goes between the values, end goes after the last one.

main.py

1print("Lamps:", 3, "Houses:", 12)2print("09", "45", sep=":")3print("Loading", end="...")4print("ready")

Output

Lamps: 3 Houses: 12
09:45
Loading...ready

Setting	What it does	If you leave it out
`sep="..."`	Goes between the values	one space
`end="..."`	Goes after the last value	a new line

Special characters

A backslash inside a string starts a short code for a character you cannot type directly:

Write	You get
`\n`	a new line
`\t`	a tab, for lining things up
`\"` or `\'`	a quote that does not end the string
`\\`	one backslash

main.py

1print("Lamp 1\nLamp 2")2print("Name:\tWick")3print("Wick said \"good night\"")

Output

Lamp 1
Lamp 2
Name:	Wick
Wick said "good night"

Comments

Python ignores everything after a # on a line. Use comments to leave notes for people, or to switch a line off without deleting it.

main.py

1# This line is a note for people2print("Lit")  # a note after code3# print("This line is switched off")

Output

Lit

Your first error

Mistakes are normal. When Python cannot run a line, it stops and tells you why. Run this:

main.py

1print("Good evening")2prnt("Lamps on")

Output

Good evening
Traceback (most recent call last):
  File "main.py", line 2, in <module>
    prnt("Lamps on")
NameError: name 'prnt' is not defined. Did you mean: 'print'?

Read an error from the bottom up. The last line names the problem: Python has never heard of prnt. The lines above say where: line 2, and show that line. Line 1 had already run, so its message is there.

Mistake	Example	Error
Missing closing quote	`print("Hi)`	`SyntaxError`
Missing parenthesis	`print("Hi"`	`SyntaxError`
Capital letter	`Print("Hi")`	`NameError`
Text without quotes	`print(Hi)`	`NameError`

A SyntaxError means Python could not read the program at all, so not even line 1 runs. A NameError happens while it runs, when Python meets a name it does not know.

Practice

Write the code, then press Check. A hint costs nothing; the answer is there when you need it.

Exercise 1

An apostrophe

Print the sentence below exactly, apostrophe included.

It should print

I'm learning Python!

exercise1.py

1# Your code here

Output

Press Run or Ctrl+Enter

Exercise 2

Tell the time

Use one print with two values and sep to show the time.

It should print

09:45

exercise2.py

1print("09", "45")

Output

Press Run or Ctrl+Enter

Exercise 3

Fix three bugs

This program has three mistakes. Fix them so it prints three lines.

It should print

Ready
Set
Go

exercise3.py

1Print("Ready")2print("Set)3print "Go"

Output

Press Run or Ctrl+Enter

What you learned

print() shows values on the screen; Python runs lines from top to bottom.
Text goes in matching quotes. Without quotes, Python works it out as code.
Commas print several values; sep and end change what goes between and after.
\n starts a new line; # starts a comment.
Read errors from the bottom up: what went wrong, then where.