Lecture I - Introduction

Programming with Python

Author
Affiliation

Dr. Tobias Vlćek

Kühne Logistics University Hamburg - Fall 2026

About this Course

About Me

Portrait photo of the lecturer, Dr. Tobias Vlćek, smiling, with glasses and a dark blazer.

  • Field: Optimizing & simulating complex systems
  • Languages of choice: Julia, Python and Rust
  • Interests: Modeling, simulations, machine learning
  • Teaching: OR, algorithms, programming & mathematics
  • More: tobiasvlcek.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 on Moodle 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 groups of three; a pair only where 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, say what a piece of code prints, fix a bug, answer a multiple-choice question
  • 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.
  • The one helper you may use is the course chatbot on the course 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 open the course chatbot on the course website
  • The chat will open and you can ask your questions
  • It is programmed by us and uses Mistral AI as backend
  • What a language model is and how it works: that is Session VI’s story, when AI switches on
  • 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
  • In Session VII we install Python (via uv) and the Zed editor on your own laptop, together in class; from Session VIII the labs run 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 every cell that depends on it: fix that cell first
  • A name is set in one cell only: set total in two and both turn red
  • 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 VII.

EP 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 never say what kind of value it is; Python figures that 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. Pick a letter, then I reveal the answer.

Answer: reassigning a name

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

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.

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

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_a/

QR code linking to the online notebook for exercise 1a, the same address as the link above.

Any questions? Let me know!

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. Pick a letter, then I reveal the answer.

Answer: type("9.99")

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

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.

Your turn

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_b/

QR code linking to the online notebook for exercise 1b, the same address as the link above.

Any questions? Let me know!

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. Pick a letter, then I reveal the answer.

Answer: 300 - 12 * 25

print(300 - 12 * 25)
0

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.

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. Pick a letter, then I reveal the answer.

Answer: 10 / 2

print(10 / 2)
5.0

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

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

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_c/

QR code linking to the online notebook for exercise 1c, the same address as the link above.

Any questions? Let me know!

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 stops with 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. Pick a letter, then I reveal the answer.

Answer: "3" + "4"

print("3" + "4")
34

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

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

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_d/

QR code linking to the online notebook for exercise 1d, the same address as the link above.

Any questions? Let me know!

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. Pick a letter, then I reveal the answer.

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

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

Your turn

Open the exercise

Scan the QR or type the link:

python.tobiasvlcek.com/notebooks/ex_01_e/

QR code linking to the online notebook for exercise 1e, the same address as the link above.

Any questions? Let me know!

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
  • 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.