Python, by Running It

About this track

Every other track on this site writes Python in its examples, and every one of them assumes you already speak it. This is where you learn it - not from reading, but from running. Every module embeds a real Python interpreter, so the code on the page is not a screenshot: you can change it and press Run and see what actually happens.

The track starts at your first print statement and works up through variables, numbers, strings, lists, conditionals and functions - the handful of ideas every later module leans on.

Every page runs real Python in the browser, with no installation and no setup. The code on screen is the code that executes, so an error you cause is a real traceback rather than a description of one.

What you will be able to do

• Write and run a program that takes input, decides something, and prints a result.
• Choose between a list, a dictionary and a string for a given job.
• Use loops and conditionals without guessing at indentation or off-by-one bounds.
• Write functions that return values, and explain why a missing return gives you None.
• Read a traceback and find the line that actually caused it.

How the track is ordered

The track starts at your first print statement and adds one idea at a time: variables and types, numbers and operators, strings and slicing, lists and indexing, booleans and comparisons, conditionals, loops, dictionaries, and functions. It ends on reading errors, which is the skill that makes everything else self-teachable. Nothing is assumed - not a prior language, not an installed interpreter, not a terminal.

Where this leads

Every other track on this site writes Python in its examples and assumes you can read it. Once functions and dictionaries are comfortable, the algorithms track is the natural next step, since its data structure pages are the same objects examined more carefully.