Lecture I - Introduction

Programming with Python

Author
Affiliation

Dr. Tobias Vlćek

Kühne Logistics University Hamburg - Fall 2026

About this Course

About me

  • Field: Optimizing and simulating complex systems
  • Languages: of choice: Julia, Python and Rust
  • Interest: Modeling, Simulations, Machine Learning
  • Teaching: OR, Algorithms, and Programming
  • Contact: vlcek@beyondsimulations.com

. . .

I really appreciate active participation and interaction!

Course Outline

  • Part I: Introduction to Programming with Python
  • Part II: Data Science Tools with Python
  • Part III: Programming Projects

. . .

Materials live in the KLU portal and are hosted at python.tobiasvlcek.com.

Passing the Course

  • Pass/fail course, 100 points in total
  • 5 in-class checkpoints × 12 points = 60 points
  • Final project + presentation = 40 points
  • You pass with 60 points and 75% attendance
  • No make-ups for missed checkpoints, but the point math absorbs one miss
  • Your project is done in pairs; solo works if the numbers don’t come out even

Checkpoints

  • Short, supervised exercises at the start of some sessions
  • Solved in the browser, just like our lab notebooks
  • ~6 small tasks each: write code, trace code, fix a bug, MCQs
  • At the end you download your .py file and upload it to Moodle
  • Session II has an ungraded 15-minute practice run (Checkpoint 0) before the lab

. . .

The weekly lab exercises rehearse exactly this routine. Do them, and the checkpoints will feel familiar.

How a session works

  • Lecture first: new concepts, with short exercises on your phone or laptop
  • Then a break
  • Then the lab: the episode’s notebook, in class, in your browser, with help in the room
  • Done early? You’re free to go. Not finished when the session ends? Keep the tab open on your laptop and finish at home

How to use AI

  • We base our assessment on the KLU classification:
    • Level 1: Pause: Use of AI defined by the educator
  • Part I (Sessions I-V) is AI-free: no Claude, ChatGPT, Mistral & Co.
  • Your sanctioned helper is the course chatbot on the learning website
  • It gives hints, not solutions, and guides your problem-solving
  • AI tools are introduced (and then allowed) in Part II, from Session VI on

. . .

Learning the basics without AI first is what lets you judge AI output later.

How to use the Chatbot

  • Just click the chatbot bubble on the website
  • The chat will open and you can ask your questions
  • It is programmed by us and uses Mistral AI as backend
  • Ask your question as specific as possible
  • This ensures enough context for the model
  • We can see aggregated logs, but cannot identify you
  • Please don’t provide personal information

No setup needed today

  • Everything in Part I runs in the browser: nothing to install
  • The lab notebooks and exercises run on marimo: click a link, start coding
  • Before Session X you install Python (via uv) and the Zed editor on your own laptop, with our guides; Session X then runs on your machine
  • Until then: a laptop, a browser, and one free account (coming up) is all you need

How a notebook works

  • A notebook is a page of cells; each cell holds a few lines of code
  • Run a cell: click into it and press Cmd/Ctrl+Enter (or the play button at its edge). The output appears right below it
  • Only edit cells that contain # YOUR CODE BELOW; the check under each exercise updates by itself
  • A red error pauses everything below it: fix that cell first
  • Save your work: Cmd/Ctrl+S, then menu (top right) → Download → Download Python code. The tab remembers you until you close it; the download is forever

One account, today: GitHub

  • Open github.com → Sign up. This takes five minutes, and we do it right now in class
  • Use an e-mail you’ll still read next year; your KLU address works well
  • Pick a username you’d be happy to show a future employer in case you might continue programming in the future
  • Already have one? Great, you’re done

. . .

Why now? From Session VI you get Zed’s paid editor plan for free as a student, and Zed only accepts GitHub accounts that are at least 30 days old. In Session X your project lives on GitHub. Nothing else to install until Session IX.

Episode 1: The Founding

A New Venture

This semester you are founding a campus food-delivery startup. Today it gets a name, a menu, and its first revenue calculation.

. . .

(Your co-founder Tobi has already spent the marketing budget on stickers.)

Variables & Types

What is a program?

  • A program is a list of instructions the computer follows
  • It runs top to bottom, one line at a time
  • Writing a program is writing that list, in a language the computer understands

. . .

Today your startup’s first program does three small things: record the founding data, do one calculation, and print a summary.

Printing output with print()

print() is a function: you hand it something, it shows it on screen.

# The line starting with # is a comment. Python ignores it
print("Welcome to your food-delivery startup!")
print("Stickers bought:", 1200)   # commas print several things, a space between
Welcome to your food-delivery startup!
Stickers bought: 1200

Variables: named values

  • A variable is a name that points to a value
  • Create one with =: name on the left, value on the right
  • You don’t declare a type; Python figures it out from the value
company_founded = 2026        # store a whole number under a name
print(company_founded)
2026

The founding data

Store the facts of the new company, then use them by name:

company_founded = 2026
first_employee = "Tobi"       # co-founder, but he put himself on the payroll first
sticker_budget = 300          # what's left after Tobi's spending spree

print(first_employee)
print(sticker_budget)
Tobi
300

Predict: Tobi buys more stickers

Tobi spends another 50 EUR of the budget. What does the last line print?

sticker_budget = 300
sticker_budget = sticker_budget - 50
print(sticker_budget)

a) Error b) 300 c) 250

. . .

Predict first. Pick a letter, then I reveal the answer.

Answer: reassigning a name

c) 250: the right side is computed first (300 - 50), then the name is pointed at the new value. A name always shows its latest value.

sticker_budget = 300
sticker_budget = sticker_budget - 50
print(sticker_budget)
250

Naming rules

  • Must start with a letter or an underscore _
  • Can contain letters, numbers and underscores
  • Case-sensitive: budget and Budget are two different names
  • Cannot be a reserved word (for, if, def, …)
  • Good names are short and meaningful for humans

. . .

Question (we solve this together, out loud): Which of these are valid variable names?
sticker_budget, 1st_employee, firstEmployee, company-name, _tobi

Your turn: 5-10 minutes

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_a/

First predict what happens, then run it.

Four basic types

Every value has a type, which decides what you can do with the value:

  • str: text, in quotes ("Tobi", "Falafel Wrap")
  • int: whole numbers (2026, 300)
  • float: decimal numbers (9.99, 0.15)
  • bool: truth values (True, False)

Checking a type with type()

type() tells you the type of any value, and it is the first thing to check when a value does not behave as expected:

print(type(2026))       # int
print(type("Tobi"))    # str
print(type(9.99))       # float
<class 'int'>
<class 'str'>
<class 'float'>

Predict: quotes around a number

Tobi typed the price with quotes. What does this print?

print(type("9.99"))

a) <class 'float'> b) <class 'int'> c) <class 'str'>

. . .

Predict first. Pick a letter, then I reveal the answer.

Answer: type("9.99")

c) str: the quotes make it text, however numeric it looks. Tobi’s “price” can’t be multiplied until it is converted to a number.

print(type("9.99"))
<class 'str'>

Your turn: 5-10 minutes

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_b/

First predict what happens, then run it.

Numbers & Arithmetic

Tobi’s 9.99 theory

Tobi’s grand plan: sell everything for 9.99. To see whether that survives contact with arithmetic, we need Python’s operators.

# margin = price - cost
print(9.99 - 7.40)
2.59

Arithmetic operators

print(9.99 + 1.50)   # addition
print(9.99 - 7.40)   # subtraction
print(9.99 * 3)      # multiplication
print(300 / 8)       # division, always gives a float
11.49
2.59
29.97
37.5

// and %: how many fit, what’s left

  • // floor division: how many whole times something fits
  • % modulo: the remainder left over
# The 300 EUR budget, boxes at 7 EUR each
print(300 // 7)      # whole boxes we can buy
print(300 % 7)       # EUR left over
print(10 // 2.5)     # 4.0: floor division on floats floors, but returns a float
42
6
4.0

Precedence: like on paper

* and / happen before + and -. Parentheses override that.

print(2 + 3 * 4)     # 14, not 20
print((2 + 3) * 4)   # 20
14
20

Predict: the sticker budget

Tobi buys 12 boxes at 25 EUR from the 300 EUR budget. What prints?

print(300 - 12 * 25)

a) 0 b) 7200 c) Error

. . .

Predict first. Pick a letter, then I reveal the answer.

Answer: 300 - 12 * 25

a) 0: 12 * 25 = 300 happens first, so the budget is wiped out. Reading left to right would give 7200, but Python follows precedence, not reading order.

print(300 - 12 * 25)
0

Predict: splitting a 10 EUR order

Two friends split a 10 EUR order. What prints?

print(10 / 2)

a) 5.0 b) 5 c) Error

. . .

Predict first. Pick a letter, then I reveal the answer.

Answer: 10 / 2

a) 5.0: / always returns a float, even when the division comes out even. For a whole number, use //.

print(10 / 2)
5.0

Whole numbers vs decimals

  • int + int stays an int; / always produces a float
  • Mixing an int and a float gives a float
  • Money is decimals, so margins are floats
margin = 9.99 - 7.40
print(margin)
print(type(margin))
2.59
<class 'float'>

round(): clean money

Division can leave a long tail of decimals. round(value, 2) keeps two. Cents.

# Split a 10 EUR order three ways
print(10 / 3)              # 3.3333333333333335, ugly
print(round(10 / 3, 2))    # 3.33, a proper amount
3.3333333333333335
3.33

Your turn: 5-10 minutes

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_c/

First predict what happens, then run it.

Strings & f-strings

The first receipt line

A string is text in quotes. Single or double quotes both work, just be consistent.

item = "Miso Ramen"
print(item)
print('Tobi shouts "9.99!"')   # mix quotes to include a quote inside
Miso Ramen
Tobi shouts "9.99!"

Concatenation, and why it hurts

You can glue strings with +, but numbers must be converted first, and it gets clumsy fast:

qty = 2
item = "Miso Ramen"
total = 23.00
print(str(qty) + "x " + item + ": " + str(total) + " EUR")
2x Miso Ramen: 23.0 EUR

. . .

(str(...) turns a value into text, which is clumsy. We’re about to see the better way.) Forget one str() and Python raises a TypeError.

Predict: adding two quantities

Tobi stored two order quantities as text and adds them up. What prints?

print("3" + "4")

a) Error b) 34 c) 7

. . .

Predict first. Pick a letter, then I reveal the answer.

Answer: "3" + "4"

b) 34: with quotes, these are strings, and + on strings glues them together. To add numbers, drop the quotes (or convert with int()).

print("3" + "4")
34

f-strings: the clean way

Put an f before the quote and write values in { }, and Python fills them in:

qty = 2
item = "Miso Ramen"
total = 23.00
print(f"{qty}x {item}: {total} EUR")
2x Miso Ramen: 23.0 EUR

. . .

No str(), no +. Just the sentence you want.

Your turn: 5-10 minutes

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_d/

First predict what happens, then run it.

Formatting money with :.2f

Inside the braces, :.2f forces two decimals, exactly what a receipt needs:

total = 23.00
print(f"{total} EUR")          # 23.0 EUR: one decimal, looks broken on a receipt
print(f"{total:.2f} EUR")      # 23.00 EUR, a proper price
23.0 EUR
23.00 EUR

. . .

Python stores 23.00 as the number 23.0. Only you know it’s money, and :.2f says so.

Multi-line receipts with \n

\n inside a string starts a new line: one string, several lines.

print(f"Falafel Wrap: 6.90 EUR\nPad Thai: 8.90 EUR")
Falafel Wrap: 6.90 EUR
Pad Thai: 8.90 EUR

Predict: braces or no braces?

What does each line print?

print(f"{2 * 3}")
print("2 * 3")

a) 6 and 6 b) 6 and 2 * 3 c) 2 * 3 and 2 * 3

. . .

Predict first. Pick a letter, then I reveal the answer.

Answer: f"{2 * 3}" vs "2 * 3"

b) 6 and 2 * 3: the f-string evaluates what’s in the braces; plain quotes keep the text literal. The f and the { } are what do the work.

print(f"{2 * 3}")
print("2 * 3")
6
2 * 3

Your turn: 5-10 minutes

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_e/

First predict what happens, then run it.

To the Lab

After the break: the lab

  • We do it together in class after a short break; whatever’s left, you finish at home
  • Head to the lab notebook: Episode 1: The Founding
  • You’ll name the company, set prices, and put Tobi’s 9.99 theory on trial
  • It runs entirely in your browser: no setup, just click and code
  • Didn’t finish the GitHub sign-up in class? Do it tonight, the 30-day clock is ticking

. . .

Download your .py before you leave. Closing the tab without downloading loses your work, and downloading is exactly how you hand in the checkpoints.

Wrap-up

Three things to remember

  1. Variables name values, and every value has a type (str, int, float, bool)
  2. Arithmetic follows precedence: * and / before + and -; round(x, 2) for money
  3. f-strings with {value:.2f} turn numbers into clean receipt lines

. . .

Next time, Episode 2: the city bans delivery after 22:00, and Tobi suggests “we just deliver yesterday’s orders.” We’ll need conditionals and loops to survive it. Plus an ungraded 15-minute practice checkpoint before the lab.

Literature

Books to start with

  • Downey, A. B. (2024). Think Python: How to think like a computer scientist (Third edition). O’Reilly. Link to free online version
  • Elter, S. (2021). Schrödinger programmiert Python: Das etwas andere Fachbuch (1. Auflage). Rheinwerk Verlag.

. . .

Think Python is a great book to start with and is free online. Schrödinger programmiert Python is a playful German-language alternative with lots of examples.

. . .

For more, see the literature list of this course.