Live Coding Session

🐍 Lists & Dictionaries, On Their Own Terms

All day you’ve used lists and dictionaries in service of something else: a list of column names to select, a dictionary to rename columns. That’s the right way to meet them, because that’s how you’ll actually use them.

Now we slow down and look at them directly, because these two containers are the backbone of Python, and twenty minutes of deliberate practice here will save you a great deal of confusion on Days 3 through 7.

How a live coding session works

We both start from an empty notebook and write everything together, live. There is no code on this page to copy, on purpose.

  • I write a line, explain it, and run it. You write the same line and run it.
  • When something breaks, we fix it together. Things will break. That’s the useful part.
  • If you fall behind, say so. Someone else is behind too, and I would much rather slow down than lose you.
  • Type the code. Do not copy it from a neighbor’s screen. The typing is the point.

Set up your notebook

  1. Create a new notebook named Session_2D_Lists_and_Dicts.ipynb.

  2. Add a title cell:

# Day 2: Session 2D - Lists & Dictionaries

Date: 09/01/2026
  1. Add the following markdown cells now, in this order, leaving space under each. We’ll fill in the code as we go, and having the structure in place means your notes stay organized instead of becoming one long scroll.
## 1. Making lists

## 2. Getting things out of a list

## 3. Changing a list

## 4. Looping over a list

## 5. Making dictionaries

## 6. Getting things out of a dictionary

## 7. Looping over a dictionary

## 8. Why this mattered today
  1. Under each heading, add an empty code cell.

That’s your scaffold. Now close this page and switch to your notebook.

What we’ll cover

Lists (about 10 minutes)

  • writing a list, and what can go in one
  • indexing from the front and from the back
  • slicing out a piece
  • len()
  • .append() to add to the end
  • looping over a list with for

Dictionaries (about 10 minutes)

  • writing a dictionary, keys and values
  • looking up a value by key
  • adding and changing entries
  • .keys() and .values()
  • looping over a dictionary
  • what happens when you ask for a key that isn’t there

Tying it back (about 5 minutes)

  • the list of column names you used in Session 2A
  • the rename dictionary you used in Session 2B
  • one small loop that checks several columns at once

What you should be able to do afterwards

  • write a list and a dictionary from scratch, without looking anything up
  • get an item out of either one, and say which container you’d choose for a given job
  • read a for loop and predict what it prints
  • explain why df[['a', 'b']] has two sets of brackets

Resources