Python is a programming language: a precise way of writing instructions that a computer can follow. You write the instructions as text, and a program called the Python interpreter reads that text and carries it out, one line at a time.

Python is popular for beginners and for coding interviews for the same reason: it reads almost like English. Here is a complete program that shows the number 5 on screen:

print(5)

That's the whole program. Languages like Java or C++ need several lines of setup to do the same thing.

What does "run" mean? When you press Run, the interpreter starts at the top of your file and executes each line. Anything you print shows up in the output panel. If the output matches what the challenge expects, you pass.

How challenges work here. Each lesson ends with a challenge. You'll see some starter code and the exact output the checker expects. Edit the code, press Run to see your output, then Submit to have it checked. Lines marked "don't modify below this line" are the test harness, so leave them alone.

A heads-up about def. From the Control Flow module on, many challenges hand you a function to fill in, like this:

def check(n):
    pass  # replace with your code

You'll learn functions properly in the Functions module, right after Loops. Until then, just write your code indented under the def line, replacing pass. The variable in the parentheses (n here) holds the test value, and the harness calls the function several times with different values. When a challenge says "return" a value, write return value as the last step.

CHALLENGEYour turn

Your output

Expected output

Test inputfed to input()