Lecture I - Introduction

Programming with Python

Author

Affiliation

Dr. Tobias Vlćek

Kühne Logistics University Hamburg - Fall 2024

About this Course

About me

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

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Tip

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

Participation

Prequisite for course Management Science (Prof. Goel)
Try actively participating in this course
You will find it much (!) easier to follow Prof. Goel
Materials will be provided in the KLU portal
Slides are hosted at beyondsimulations.github.io/Introduction-to-Python

Teaching

Lecture: Presentation of tools and concepts, based on small examples and code snippets
Tutorial: Hands-on examples to be solved in groups
Difficulty: Difficult at first, but gradually easier

Passing the Course

Pass/fail course
75% attendance required for passing the course
2 assignments and 1 little project
You will be given programming exercises to solve
You can group up (3 students) and work together
Each student group submits one solution

Solution

Provide a code solution to the problem (.py files)
Code files need to be executable
Detailed explanations of your code should be provided
Use comments or docstrings in your code
Provide a general (verbal) introduction to each problem

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Tip

I’d encourage you to start and submit your solution early

Difficulty of the Course

We’ll cover the basics of programming (in Python) at first
This is similar to learning a new foreign language
First, you have to get used to the language and learn words
Later, you’ll be able to apply it and see results
Similar to learning a language: Practice, practice, practice!

What to expect

Some investment in the beginning to see the return later
You can ask questions and get support anytime
After completion, you will be able to read code
and write your own program using Python
That’s quite something!

Goals of the Course

Essential concepts and tools of modern programming
Automated solutions for recurrent tasks
Algorithm-based solutions of complex problems
Usage of AI in a specific context

Python as Language

Origins: Conceived in late 1980s as a teaching and scripting language
Simple Syntax: Python’s syntax is straightforward and easy to learn
Versatility: Used in web development, data analysis, artificial intelligence, and more
Community Support: A large community of users and extensive documentation

Help from AI

You are allowed to use AI (GitHub Copilot, ChatGPT, LLama3 …)
These new tools are really powerful for learning Python!
They can help you a lot to get started with programming

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Warning

But you should not simply use them to replace your learning.

Why learn programming?

Analytics

Research

Visualization

Finance

Logistics

How to learn programming

My Recommendation

Be present: Attend the lecture and participate
Put in some work: Repeat lecture notes and try to understand the examples yourself
Do coding: Run code examples on your own, play around, google, modify, and solve problems on your own

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Tip

Great resources to start are books and small challenges. You can find a list of book recommendations at the end of the lecture. Small challenges to solve can for example be found on Codewars.

Don’t give up!

Programming is problem solving, don’t get frustrated!
Expect to stretch your comfort zone

Learning Path

The learning path can be quite steep!
First of all help each other!
Try to find help in lecture materials and books, the Python documentation, and online (e.g. Google, ChatGPT, StackOverflow, …)
In case you get frustrated, read the following helpful blog post about the challenges on medium.com

Errors

In case you find errors and typos in the lecture notes, please report them in the following form:
https://tally.so/r/w7oapa

Setting up Python

Install Python

Sources are the Python website or Anaconda
But I would recommend we start by installing Thonny
An open source IDE running on Windows, Linux and Mac
Built in Python interpreter and package management!

What is an IDE?

Integrated Development Environment = application
It allows you to write, run and debug code scripts
Thonny is an IDE specifically for Python beginners
It is easy to use as beginner!
Other IDEs include for example PyCharm from JetBrains or Visual Studio Code from Microsoft

Thonny

Python on iPads

Although you can run Python scripts from on your iPad, it is not recommended for the course
Nonetheless, you could use Pythonista
It works locally on your iPad and can run most scripts

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Caution

Not all packages available in Python are available in Pythonista, thus you might need a computer to solve certain problems.

First start of Pythonista

Your first code

Hello, World!

Task: Create a directory for the course and create a new file called hello_world.py with the following code:

# This is a comment in Python
print("Hello, World!")

Hello, World!

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Run it with the green ‘run’ button or by pressing F5!

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Note

“Hello world” is a classic example to start with. It is often used as a test to check if your computer is working properly and that you have installed the necessary software.

Hello, World in a Message

Task: Change the code in your hello_world.py file. Assign the string "Hello, World!" to a variable called message and print the variable.

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Use the equals sign (=)
Variable name goes on the left
Value to be assigned goes on the right

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# Here we assign the string "Hello, World!" to variable message and print it
message = "Hello, World!"
print(message)

Hello, World!

Hello, World in Parentheses

We can also mix " and ' in a string, if we are consistent:

# This code works
message = 'I shout "Hello, World!"'
print(message)

I shout "Hello, World!"

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# This code does not!
message = 'I shout 'Hello, World!""
print(message)

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Try it yourself! What does happen, if you try to run it?

First Errors

SyntaxError: invalid syntax

The code is not valid Python syntax
Likely the most common error that you will encounter!
Happens when you make a mistake, e.g., illegal character, missing a colon, parentheses or quotations
You can fix this by correcting the code and re-running
In the lecture you will encounter many more errors!

Program

What is a Program?

Sequence of instructions telling a computer what to do
Written in a language the computer can understand
Basic operations in most languages:
- Input: Data from keyboard, file, network, sensors, etc.
- Output: Display data, save it, send over network, etc.
- Processing: Perform calculations, analyze data, make decisions, find patterns, etc.

Key concepts

Key concepts in most languages:
- Variables: Store and manipulate data
- Conditional execution: Check and execute accordingly
- Loops: Perform actions repeatedly
- Functions: Group instructions for reusability

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Note

We will cover these concepts in more detail later in the course.

How Python executes code

Python is an interpreted language
The source code is executed line by line
The interpreter checks the syntax and executes the code
This is in contrast to compiled languages, where the code is compiled into machine code before execution

Hello again, World!

Let’s go back to our first program:

# Our first program
message = "Hello, World!"
print(message)

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Comment: In the first line we define a comment with #
Variable: In the second we define a variable message
Function: In the third line we call a function print

Don’t worry!

Already confused? Don’t worry about it for now!
We’ll learn more about variables and functions later

Python’s Syntax

The Zen of Python

Python’s name originally comes from Monty Python
Style is based on a philosophy called Zen of Python
Collection of 19 statements with general principles

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Task: Try this code in Python:

# Try this code in Python to see the Zen of Python
import this

Variables

A variable in Python is a name that points to a value
Created by using the assignment operator =
Python does not require a declaration of variable types

a = 2 # Variable a assigned the value 2
b = "Time" # Variable b assigned the value "Time"
c = print # Variable c assigned the print function
c(b) # Now we can call the print function with c

Time

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But there are certain rules to variable names!

Variable Naming Conventions

Must start with a letter or underscore _
Can contain letters, numbers and underscores
Names are case sensitive, e.g., a and A are different!
Cannot be a reserved word, e.g., for, if, def, etc
Good names are short and meaningful for humans!

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Question: Which of the following fulfill these conditions?
a, _duration, 1x, time_left, 1_minute, oneWorld, xy4792

Functions

Functions are named blocks of code
Can take arguments function([arguments])
Can return results or None

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# Print is such a function
print("Hello, World!") # It takes an argument and prints it to the console
print("Hello","World!", sep=", ") # It can also take multiple arguments

Hello, World!
Hello, World!

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Note

We will cover functions in more detail later in the course.

Values and Types

What are Values and Types?

Value: Fundamental thing that a program manipulates
- In Python, values are either numbers or strings
Type: Type of a value
- Determines what operations can be performed on it
- type() is a function that returns the type of a value
- Takes one argument and returns its type as string

Strings

Back to our example of “Hello, World!”

# We define the variable message and assign it the value "Hello, World!"
message = "Hello, World!"

# We save its type in another variable called message_type
message_type = type(message)

# We print the value of our new variable
print(f"{message} is a {message_type}")

Hello, World! is a <class 'str'>

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Result: “Hello, World” is a string - in short ‘str’.

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But what about the f”?

Formated Strings

f-strings are strings that start with f
They contain expressions, e.g., variables, in braces
Evaluated at run time and inserted into the string

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Note

In older code bases, f strings were not available. Here, interpolation could be done as shown below with print() and .format(). But this method is less concise and arguably less readable.

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print("{} is a {}".format(message, message_type))

Hello, World! is a <class 'str'>

Specifying Formatted Strings

We can further specify their forman with {<to_print>:<width>.<precision>f}
width can be a number specifying the output width
<, ^, > can be used before the width to align the text
precision can be used to specify the decimals
.f can be used to format floats

x = "hello"
print(f"{x:<10} has {len(x):>10.2f} characters.")

hello      has       5.00 characters.

Expressions

Produce a value when evaluated
Can be used as part of larger expressions or statements
Statements are expressions that don’t produce a value
Examples: arithmetic operations, function calls, variables

x = 1 # Statement that assigns the value 3 to x
y = x + 2 # Expression on the right side assigned to a variable y
print(f"Great, the result is {y}")

Great, the result is 3

A step back: What is a String?

Remember: “Hello, World” is a string - in short ‘str’
A string is a sequence of characters enclosed in quotes
Examples: "Hello", 'World', "123", '1World23'

hello = "Hello"
world = 'World!'
print(hello,world,sep=", ") # We can specify the separator with the argument sep

Hello, World!

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Note

Strings are immutable, we can’t change characters in them once created.

String Operations

But we can also do much more with strings!
String concatenation, indexing, slicing, length, etc.

two_strings = "Hello" + ", " + "World!" # String concatenation
print(two_strings)

Hello, World!

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print(two_strings[0]) # Indexing starts at zero!

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print(len(two_strings)) # With len we can find the length of our string

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print("--x--"*3) # We can also repeat strings

--x----x----x--

Booleans

Booleans represent two values: True and False
Internally they are represented as 1 and 0, respectively
They are used for logical operations and control flow
E.g.: if, while, for, elif, `else

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x = True
y = False
print(x)
print(type(y))

True
<class 'bool'>

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> More on them in our next lecture!

Integers and Floats

Integers are whole numbers, e.g.: 1, -3, 0 or 100
Floats are decimal numbers, e.g.: -4.78, 0.1 or 1.23e2
Bit size is not specified (e.g.: 64 bits) in Python!

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x = 1; y = 1.2864e2 # We can separate multiple operations in one line with semicolons
print(f"{x} is of type {type(x)}, {y} is of type {type(y)}")

1 is of type <class 'int'>, 128.64 is of type <class 'float'>

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Warning

The interpreter will automatically convert booleans to integers to floats when necessary, but not the other way around!

First Functions and Operators

Arithmetic operators

addition = 1 + 2;           print(f"Result: addition is {addition}")
substraction = 1 - 2;       print(f"Result: substraction is {substraction}")
multiplication = 3 * 4;     print(f"Result: multiplication is {multiplication}")
division = 7 / 4;           print(f"Result: division is {division}")
floor_division = 7 // 4;    print(f"Result: floor_division is {floor_division}")
exponentiation = 9 ** 0.5;  print(f"Result: exponentiation is {exponentiation}")
modulo = 10 % 3;            print(f"Result: modulo is {modulo}")

Result: addition is 3
Result: substraction is -1
Result: multiplication is 12
Result: division is 1.75
Result: floor_division is 1
Result: exponentiation is 3.0
Result: modulo is 1

Precedence

Operators are the same as in most other languages
Can be combined with each other and variables
Normal rules of precedence apply

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# Operator precedence works as on paper
combined_operation = 2 + 3 * 4
print(f"2 + 3 * 4 = {combined_operation}")

2 + 3 * 4 = 14

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# Parentheses change precedence as expected
parentheses_operation = (2 + 3) * 4
print(f"(2 + 3) * 4 = {parentheses_operation}")

(2 + 3) * 4 = 20

The input() Function

Used to get user input as string from the console
Syntax: input([userprompt])
Displays optional prompt and waits for user input

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name = input("What's your name? ")
print(f"Hello, {name}!")

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Important

The function always returns the input as string!

Input in Action

Task: Solve the following task:

# TODO: Ask the user for their age and print a compliment

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Solution

age = int(input("How old are you? "))
print(f"You look great for {age}!")

Type Conversion

Use type conversion for other data types

Integer: int(input())
Float: float(input())
Boolean: bool(input())
String: str(input())

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# Converting to Integer
age = int(input("Enter your age: "))
next_year = age + 1
print(f"Next year, you'll be {next_year}")

The round() Function

# Hence, we can use the int() function to convert a float into an int
soon_int = 1.789
print(f"{soon_int} converted to {int(soon_int)} of type {type(int(soon_int))}")

1.789 converted to 1 of type <class 'int'>

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# We can also use `round()` to round a float to an int
soon_int = 1.789
print(f"{soon_int} converted to {round(soon_int)} of type {type(round(soon_int))}")

1.789 converted to 2 of type <class 'int'>

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# Or to a float with a certain number of decimals
no_int = 1.789
print(f"{no_int} converted to {round(no_int,1)} of type {type(round(no_int,1))}")

1.789 converted to 1.8 of type <class 'float'>

Questions?

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Note

That’s it for todays lecture!
We now have covered the basics on the Python syntax, variables, and data types.

Literature

Interesting Books to start

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.

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Note

Think Python is a great book to start with. It’s available online for free here. Schrödinger Programmiert Python is a great alternative for German students, as it is a very playful introduction to programming with lots of examples.

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For more interesting literature to learn more about Python, take a look at the literature list of this course.