Cheat sheet

Everything we used today, on one page. Print it or keep it open in a tab.

JupyterLab keys

Key What it does In Colab

Run the cell and move to the next one Same

Run the cell and stay on it Same
and Esc is command mode, for whole cells. Enter is edit mode, for typing. Same
and (command mode) Add a cell above or below + Code and + Text
and (command mode) Make the cell markdown or code , then M or Y
(command mode) Delete the cell. Z undoes it. , then D

Save Saves to Drive by itself
len? Show help for len. Works for any name. Same
Run → Run All Above Selected Cell Run every cell above the current one Runtime → Run before
Kernel → Restart Kernel… Start fresh. Run your cells again. Runtime → Restart session

Only the last line of a cell shows its value. Use print() to show more.

Variables and types

Code What it does
age = 34 Store a value. One = assigns.
age == 34 Compare two values. Two == ask a question and give True or False.
type(age) Show the data type: int, float, str, bool, list, dict
f"I am {age}" Put a value inside text (an f-string)

Names use letters, digits (0-9) and _, and can’t start with a digit.

Strings and indexing

Counting starts at 0.

Code Result with word = "python"
word[0] 'p'
word[-1] 'n'
word[0:3] 'pyt' (the end index is left out)
len(word) 6

Lists

Code What it does
toys = ["feather", "string"] Make a list
toys[0] Get an item by position
toys[0] = "laser" Replace an item
toys[0:2] Slice: items 0 and 1
toys.append("catnip") Add to the end. Changes the list itself.

Dictionaries

Code What it does
birthdays = {"Spot": "May 1"} Make a dictionary of key: value pairs
birthdays["Spot"] Get a value by key
birthdays["Sparky"] = "May 10" Add or change a pair

[] on a list takes a position. [] on a dictionary takes a key.

Operators

Kind Operators
Arithmetic + - * / (always a float) // (floor division) ** (power) % (remainder)
Comparison == != < > <= >=
Logical and or not

if, for and def

if score >= 90:
    print("A")
elif score >= 80:
    print("B")
else:
    print("Keep going")
for i in range(5):
    print(i)

for name in ["Bob", "Bill"]:
    print(name, len(name))
def add_nums(a, b):
    return a + b

total = add_nums(2, 3)

The colon and the indented lines belong to each other. print shows a value; return hands it back.

Methods

Dot notation: object.method(argument).

Kind Example What happens
String method word.upper() Returns a new value. word is unchanged.
List method toys.append("catnip") Changes the list itself. Run it twice and you get two.

Common errors

Error Usually means Fix
NameError A name doesn’t exist yet Check the spelling, and run the cell that creates it
SyntaxError Python can’t read the line Look for a missing quote, bracket or colon
IndentationError The indented lines don’t line up Use the same number of spaces in the block
TypeError A value is the wrong type for the operation Check with type(), such as "5" + 5
IndexError The position doesn’t exist Remember the last index is len(x) - 1
KeyError The key isn’t in the dictionary Check the spelling and capitalization

Read the last line of the message first: it names the error. The lines above it point to where it happened.

uv and conda commands

Task uv conda
Check it’s installed uv --version conda --version
Make the project uv init --python 3.13 --vcs none --no-package dss-python conda create -y -n dss-python -c conda-forge --override-channels python=3.13 jupyterlab matplotlib (also adds JupyterLab and matplotlib)
Add JupyterLab and matplotlib cd dss-python, then uv add jupyterlab matplotlib Done by the line above
Start JupyterLab (run it inside dss-python) uv run jupyter lab conda activate dss-python, cd dss-python, then jupyter lab
Add any package, such as Polars for the EDA workshop uv add polars conda install -c conda-forge --override-channels polars

With conda, make the folder once with mkdir dss-python before the first cd dss-python.

Checked with uv 0.13.3 on October 20, 2026. The uv docs and the conda docs are the latest word.