Module 01 - Programming, with Python

Why learning (even a little) programming is good for you #

• Learn how to solve problems, how to solve YOUR business problems!
• Develop new skills:
  • Build up intuition and analytic thinking about processes (reusable in many contexts!)
  • Automate repetitive, error-prone tasks and business procedures (saving time!)
  • Analyze real world datasets efficiently, allowing good decision making
  • Use and master existing tools/apps, in more advanced ways (e.g. spreadsheets)
• You culture! Better understand how things work
• Programming is a creative activity, like drawing or writing
• It’s fun (believe me)!

Software is everywhere, not a day goes by without you interacting with software

What programming will teach you #

Learn to get better at:

• Designing :
  • Analyze: decompose big problems in smaller solvable problems
  • Find the right problem to solve
  • Give shape to the good solution to the right problem
  • Think about edge cases
• Communicating your ideas
• Testing your ideas: Prototyping, Modeling, Quick feedback loop
• Handling failures!: The world is a mess, there will be failures! Anticipate what can go wrong
• Specifying a solution with good abstractions (e.g. writing better prompts for a LLM!)

Later, every time you encounter a new problem, ask yourself this question: “How would I solve it by writing a program?”

Programming vs coding #

“People confuse programming with coding. Coding is to programming what’s typing is to writing.” (Leslie Lamport)

What is coding ? (Oxford Dictionary) #

“To convert into a code. To express in an indirect way. To encode”

• Translation in a specific symbol system
• To reify preexisting careful toughts (crafting a story, developing an argument, designing a step-by-step procedure, etc.)

What is programming ? (Oxford Dictionary) #

“To apply a set of instructions to control the behavior of a computer”

• It’s not about syntax or language or code
• It’s about control, logic and behavior

Programming vs Coding #

• Programming: Find and describe an automated process that solves a given problem. How to knowledge.
• Coding: Translate a process into a language the computer can understand

Coding is cheap (especially in the era of gen AI), programming isn’t! Or is it? While coding, many things happen in your brain! Coding can not really be reduced to “typing characters on a keyboard”. Nevertheless, writing code is a part of a broader activity we call programming

Programming without coding #

• You can program without coding (and maybe you already did) !
• Visual programming/NoCode tools:
  • Automation platforms/Workflows: Make, Zappier, n8n, etc.
  • Applications: Scratch, Airtable, etc.
  • Spreadsheets (Excel, Libre Office, etc.)

There is (and always be!) code underneath…But it’s not your problem!

Programming is not (really) about computers #

“Computer science is a terrible name for this business… First of all, it’s not a science… It’s also not really very much about computers” (Harold Abelson, MIT 6.001 Structure and Interpretation, 1986). Watch the first episode of this course to have a wonderful introduction to programming

Programming is about processes, building how-to knowledge.

Example of a program #

We want to solve this problem:

Find the youngest person into a group.

Two steps work #

1. Find the correct process
2. Program a computer to execute it

Find the process #

We have to design (or find) a step-by-step process (instructions) to solve this problem.

Find the youngest person program, first try #

1. For each person in the group:
   1. Ask for their birth date and their name.
   2. If their birth date is more recent than the previous youngest person’s (or if it’s the first person we ask), consider this person the youngest person in the group.

First analysis #

• We have to remember “somehow” whose birth date is the most recent and which person is the youngest during the process, in order to give the correct answer at the end: we need memory.
• We need to name data to identify them correctly.

Let’s do this again using a piece of paper as memory, to keep track of the correct answer.

Find the youngest person program, second try #

1. Take a piece of paper and write none for “Youngest Person” and “Birthdate”.
2. For each person in the group:
   1. Ask for their birth date and their name.
   2. If their birth date is more recent than the one written on the paper (or if it’s the first person), update the paper: erase the old info and write down this new person’s name and birth date.
3. Show the name written on the paper.

Find the youngest person program, a graphical view #

Analysis #

• This is what we can call Pseudo-code or Structured english (For each, If, Update, Erase, etc.). This program can not be (yet!) executed by a computer, because computers does not speak english
• Our piece of paper = memory (read and write to it)
• Youngest Person and Birthdate are what we call variables:
  • They have a name (unique identifier)
  • They store some data during the process

Our procedure has two parts: Data and Instructions #

Notice that our program is made of two different parts:

• Data: “Birth Date”, “Name” are data. It’s facts, information, values. It doesn’t do anything.
• Actions/Instructions: “For each”, “if”, “update the paper”, “ask for” are instructions, actions to perform. Instructions are executable.

Turn our procedure into a program #

Once figured it out, we can code (encode, translate) this procudre into a programming language, like the Python language (or any other language!), to automate its execution with a computer.

An automated procedure is what we call a program.

Any program can be encoded into different programming languages

Why turning our procedure into a program? #

Because we want:

• The process to be automated. Once initiated, the process runs completely autonomously without requiring any human intervention.
• To execute this procedure as many times as needed, adapting to any group size or volume, no human error!
• To let the computer do all the work, so we can focus on high-value tasks.

In short: time savings, no human error and flexibility.

What could go wrong in the manual procedure? #

• Misspell names or birth dates
• Lack of data (someone forgot…)
• Incomplete process: I forgot to ask someone
• Edge cases: two persons could be born on the same day! Need to ask for more precise information? Choose one? Print both?
• Etc.

Programming is like life: if things can go wrong, (given enough time) they will go wrong!

How to turn our procedure into a program? #

• We need to load our procedure (data and instructions) into the computer (somehow!)
• But computers do not understand english (or any human language)!
• We need to translate it to a code (symbol system) a computer can understand.
• What is the language of the machine? How do we tell the computer to execute our procedure?
• How do we program the computer?

But first, what is (really) a computer? #

How do we program the computer?

To answer this question, a few words about computers:

• What they are
• How they work

Properties of a modern computer #

• What your need to know about computers, they are:
  • Stupid: They can only do simple operations with binary data: Read, Write, Add, Subtract, Multiply, Compare,… This is what we call computing
  • “Fast” (compared to us): They can do it billions of times per second (GHz).

Note: They are still “slow” compared to biological systems like cells, where billions of complex chemical reactions happen in parallel.

What is a computer ? #

• Computers are electronic machines able to execute very simple operations
• Computers only understand binary code, called Machine code
• Machine code is binary patterns that encodes signals for the hardware to activate specific circuits and execute specific actions (Read, Write, Add, Compare, etc.). This correspondence is called the Instruction Set Architecture (ISA)
• Each machine (CPU) has its own Instruction Set.

Ex: 00010101 10110101 machine code for a given machine could result in the action “write the value $5$ to memory” or “compare 72 to 16”.

Bits don’t Byte #

• Bit:
  • Short for binary digit. The fundamental block of information. A bit can only be one of two values: 0 or 1.
  • With a base-2 symbol system, called binary, you can say/encode anything!
• Byte (computer):
  • Group of 8 bits
  • The basic unit of memory computers work with (read/write)

1 byte gives $2^8=256$ unique codes to represent 256 different values (from $00000000$ to $11111111$), for example numbers from 0 to 255.

Computer architecture #

• Designed in the 1940s by John von Neumann
• Von Neumann Architecture is based on a core principle: data and programs are stored in the same main memory (in binary)

Von Neumann architecture remains the standard computer architecture used today!

Prior, machines required physical rewiring to switch programs (One problem to solve = One machine). The Von Neumann architecture allows computers to run any program simply by loading new binary instructions into memory! This is Software!

Fundamentals of Von Neumann Architecture #

Computers has four major components:

• Central Processing Unit (CPU): Decodes and executes instructions. Read/Write from/to memory
• Random Access Memory (RAM): Giant array of numbered bytes (each byte has an address). Stores instructions and data
• Input and Output devices (I/O): Used to interact with the outside world (keyboard, screen, hard drive, sensors, network card, etc.).

Execution cycle (simplified) #

1. Fetch: CPU reads next machine code instruction, from a program loaded in memory
2. Decode what kind of instruction
3. Execute: sequence of actions to perform the instruction (ex: Add, Compare, etc.), defined by the instruction set of the CPU.
4. Write: write the result back to memory
5. Go back to step 1.

At the end, memory changes (bytes are written, new values are created): program execution

The CPU clock sets the pace, ticking billions of times per second (GHz) to trigger each step of the fetch-decode-execute cycle.

What is program execution at low level (machine level) #

• A program consists of a sequence of binary instructions that drives the memory from an initial state to a desired target state
• The desired target state is the result of the program (e.g. write the correct name of the youngest person on the screen!)

How to store our program (our anything) in computer memory? #

Computer memory is a giant array of bytes (8-bit boxes)

How to put things into computer memory?

We need to encode things in binary, using well defined encoding systems.

Encoding things in binary, some examples #

#Integers
1           -> 00000001                                (1 byte integer)
2           -> 00000010
255         -> 11111111

#Decimal (floating point number)
3.14        -> 01000000 01001000 11110101 11000011     (32-bit Float: Sign + Exponent + Mantissa)

#Text: different encoding systems exist
'A'         -> 01000001                                (in ASCII) 
'😀'        -> 11110000 10011111 10011000 10000000     (in UTF-8)

#Pixel: every pixel consists of 3 bytes for Red, Green and Blue colors:
Pure Red    -> 11111111 00000000 00000000              (RGB, 3 bytes: R=255, G=0, B=0)
Pure Blue   -> 00000000 00000000 11111111              (RGB, 3 bytes: R=0, G=0, B=255)

#Image: A big array of pixels 
11111111 00000000 00000000 11111111 00000000 11111111 00000000 00000000 11111111 00000000 00000000 
00000000 11111111 00000000 00000000...

#Movie : A big array of images...

Everything (text, photos, programs, etc.) is ultimately just (m|b)illions of zeros and ones (binary data) being manipulated by hardware components

How to store a bit (for real!): a few examples of binary objects #

• A bit is an abstract concept representing a choice between two mutually exclusive states: $0$ or $1$
• Computers need real binary objects to have a memory and store binary data and machine code
• A bit can be stored by a digital device or other physical system that exists in either of two possible distinct states.

Beacons of Gondor #

Important binary objects

• Unlit (0): Gondor is not in trouble apparently
• Lit (1): Gondor is in big trouble!

Candle #

• Lit (1), Unlit (0)

For many obvious reasons, computers don’t use candles for storing bits

Vacuum tube #

• Conducting (1), Non-conducting (0)
• Read/write access time: ~10 microseconds
• Bit size: ~10 cm
• Hard to produce, Unreliable (short lifetime), Expensive to manufacture (around $100 per unit in the 1940s!), High power consumption!

Magnetic tore (e.g. used by Apollo Guidance Computer) #

• Magnetic Field direction: Up (1), Down (0)
• Read/write access time: ~10 microseconds
• Bit size: ~1 mm
• More reliable, Lower power consumption, Less fragile than vacuum tubes, Handle Radiations!

Total Apollo Guidance Computer memory was 4 KB. AGC is real software engineering

Transistor (used in modern computers!) #

Typical Dynamic RAM module (Corsair DDR2-533) :

• Charged(1), discharged(0)
• Based on billions of tiny binary objects (memory cells 1T1C)
• Read/write access time: ~10 ns
• Bit size: ~10 nanometers !

Reminder #

• What do the following prefixes mean: Kilo, Mega, Giga?
  • Kilo: $10^3$ (thousand)
  • Mega: $10^6$ (million)
  • Giga: $10^9$ (billion)
• What is a Hertz? Unit of frequency, 1 Hz = 1 cycle per second. E.g., a clock that ticks once per second = 1 Hz.

40’s/50’s - Mainframes : ENIAC #

ENIAC, 1945-1950 (USA)

• First fully electronic computer!
• Could solve, in principle, any numerical computing problem
• Follows the Von Neumann architecture
• Weights 27 tons and spans 170 square meters! (uses 18,000 vacuum tubes!)

Evolution of Computing: From the 1940s to Today 1/2 #

Evolution of Computing: From the 1950s to Today 2/2 #

Today, a modern mainstream laptop, such as a Lenovo ThinkPad:

• is roughly a million times faster (billions of instructions per second);
• has ten million times more RAM;
• costs about 1 million times less to produce;

than a computer like the 1945 ENIAC (the first fully programmable computer)!

Welcome to the Space Age!

What has changed over 80 years #

• Machine power: today, they execute billions of instructions per second.
• Memory capacity: multiplied by millions, giving users the “impression” of almost infinite memory*.

What has BARELY/NOT changed over 80 years #

• Fundamental architecture: modern computers still follow the Von Neumann model (a single memory for both data and instructions, a processing unit and a control unit);
• How we program machines: our programming languages and concepts remain nearly unchanged, even though hardware has evolved drastically.

How to encode our procedure ? 1/2 #

• Our procedure must be encoded in Machine code (binary) to be loaded and executable by the computer
• But, we have the choice, at which level of abstraction we want to code our procedure, we can use either:
  • Machine code directly! Ouch…
  • Lower level languages, like Assembly languages, close to machine code
  • Higher level languages to write human friendly code, and use tools to translate it to machine code.

How to encode our procedure ? 2/2 #

^  -> Python, PHP, Lisp, Java, R, Fortran, etc.
|  ----------------------
|  Higher level languages (closer to humans)
|  ----------------------
|  - C Language : on the border between lower and higher level languages
|  ---------------------
|  Lower level languages  (closer to hardware)
|  ---------------------
|  - Assembly languages (last human readable programming language before binary)
|  - Machine code (just bits)

Same program, different codes, an example #

Let see the same program written in different codes:

• Machine Code: binary instructions the CPU can process directly
• Assembly Code: last human readable programming language before binary
• C code: at the interface between lower and higher level languages
• Python code (what we will use!): an example of higher level language

Example of Machine code (lowest level language) #

01111111 01000101 01001100 01000110 00000010 00000001
00000001 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000011 00000000
00111110 00000000 00000001 00000000 00000000 00000000
01010000 00010000 00000000 00000000 00000000 00000000
00000000 00000000 01000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 10011000 00110110
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 01000000 00000000
00111000 00000000 00001101 00000000 01000000 00000000
00011111 00000000 00011110 00000000 00000110 00000000

Example of Assembly Code (low level language) #

.LC0:
 .string "c=%d"
 .text
 .globl main
 .type main, @function
main:
.LFB0:
 .cfi_startproc
 pushq %rbp
 .cfi_def_cfa_offset 16
 .cfi_offset 6, -16
 movq %rsp, %rbp
 .cfi_def_cfa_register 6
 subq $16, %rsp
 movl $2, -4(%rbp)
 movl $21, -8(%rbp)
 movl -4(%rbp), %eax
 imull -8(%rbp), %eax
 movl %eax, -12(%rbp)
 movl -12(%rbp), %eax
 movl %eax, %esi
 leaq .LC0(%rip), %rax
 movq %rax, %rdi
 movl $0, %eax
 call printf@PLT
 movl $0, %eax
 leave
 .cfi_def_cfa 7, 8
 ret
 .cfi_endproc

Example of C code (“higher” level language) #

#include<stdio.h>

int main(){
    int a = 2;
    int b = 21;
    int c = a * b;
    printf("c=%d", c);
}

Example of Python code (higher level language) #

a = 2
b = 21
c = a * b
print(f"c={c}")

Which programming language to choose? #

As always, it depends on what you want to do!

There are more than 8000 programming languages available today. Almost all of them allow you to write any kind of program.

However, programming languages differ in their properties, advantages, and application domain. Programming languages can be:

• High-level or Low-level
• Interpreted or compiled
• General purpose or domain-specific

Lower level languages #

Hardware details are exposed (CPU architecture, registers, memory addresses). Memory is managed explicitly. Perfect for embedded systems. Examples: Assembly languages, C/C++ (from a modern perspective).

• Pros:
  • Performance and optimization: Direct control over execution speed and resource usage (Manual Memory Management)
  • What you write is (almost) directly what the hardware executes
  • Interact directly with hardware interfaces
• Cons:
  • Need to compile to every CPU architecture (ISA)
  • Must understand computer (CPU) architecture.
  • Manual Memory Management

Higher level languages #

Abstract away hardware details. Focus on problem-solving logic rather than how the computer works (CPU, RAM). Examples: Java, JavaScript, Lisp, Python!, etc.

• Pros:
  • “Closer” to the problem to solve, stronger abstractions (loops, data structures, procedures/functions, modules, etc.), more human friendly
  • Portability: Write once, run anywhere (cross-platform*).
  • Automatic Memory Management via Garbage Collection and automatic allocation.
• Cons:
  • Slower execution speed and higher RAM usage.
  • Hardware is hidden behind layers of abstraction.

Python IS higher level language

Interpreted and Compiled languages #

• Compiled languages : the entire high-level program is transformed directly into Machine Code (01001000...) by a compiler prior to running. Produces an executable file tailored directly to the CPU instruction set, yielding maximum execution performance and determinism. Examples: C, C++, Fortran, Go, Rust
• Interpreted languages : a pre-compiled program, called an interpreter, reads and translates code line by line into intermediate code (bytecode), executing instructions dynamically on the fly. Offers flexibility and ease of development, but adds a translation layer above hardware execution and requires to load the interpreter in memory. Examples: Lisp, PHP, JavaScript, Python

Python IS an interpreted language

Python #

In this course, we will use the Python Programming language to write our programs.

We need to learn its language syntax. It will be our vessel to explore programming.

Syntax changes slightly from one language to another, concepts and fundamentals don’t! Without knowing, by learning Python, you will be learning many other languages at the same time!

Python in short #

• Created in 1989 by Guido Van Rossum(Netherlands). Version 1 released in 1991
• Version 3+ (today), released in 2008
• Qualities :
  • Easy to read, to learn
  • General purpose
  • High level, Interpreted (Cross-platform!), Dynamic
  • Multi-paradigms (procedural, functional, object-oriented)
  • Huge community, documentation and learning materials!
  • Lot! of specialized libraries/modules: GUI (PyGTK), Mathematics/Computing (NumPy, SciPy), Machine Learning (TensorFlow), Deep Learning (Pytorch), Data Visualisation (Matplotlib), Data Analysis (Pandas), etc.

Python is an excellent language to learn programming!

What you can do with Python? #

Python is a general purpose programming language. It’s used:

• For teaching/learning programming (schools)
• By the scientific community (Physics, Biology, etc.) (with Fortran, R)
• For Machine/Deep learning, Data Sciences and Artificial Intelligence (advanced and complex libraries)
• For writing scripts and automating any kind of tasks
• To develop complete web applications, desktop applications and video games
• In Excel spreadsheets!

It’s a good choice!

Python is an interpreted language #

A special program, called the Python Interpreter will translates and executes our Python code into machine code

Setting up our programming environnement 1/2 #

What we need:

• The Python interpreter, to run our programs!
• Package manager to install useful packages later on
• Rich text editor to write and read code
• A terminal

Setting up our programming environnement 2/2 #

We will use the PyCharm, an Integrated Development Environment (IDE), maintained by Jet Brains (Community Version).

1. Download and install PyCharm on your machine.
2. Launch PyCharm
3. Create a new script script.py and run it. See the result in the terminal.

Why use PyCharm ? #

• Community version is free
• Beginner friendly, no configuration, everything at one place
• Cross-platform (Windows, macOS, GNU/Linux)
• Manage and install the Python Interpreter, Package manager and useful/powerful packages/modules (for later) to write (even more) interesting programs!
• Smart code editor with autocompletion and color highlight syntax
• Jupyler Notebook Integration
• Useful developer tools: debugger, terminal, etc.

PyCharm is a sophisticated program! We will only use basic functionalities for this course.

Programming in PyCharm #

• Programs are written in files called scripts, with a .py extension (by convention).
• To run a program, we only have to call the Python interpreter (Play button in PyCharm):

# In the terminal, inspect Python version installed (3+)
python -V
Python 3.14.7
# Run a program written in my_program.py
python my_program.py

Be sure to be able to master the full cycle: write/read code, run your program, see the output

Our “Find the youngest person in the group” program… in Python #

Disclaimer:

• Try to get the big picture of the following code (the different parts and the role of each section)
• There are a lot of details! It’s completely normal if you don’t understand everything for now, don’t worry!

At the end of the next module you will be able to write such programs yourself!

Run “Find the youngest person in the group” program #

1. Copy/Paste the program in a new script called find_youngest.py
2. Run it in PyCharm and check the result in the terminal

group = {
    "Alice": "1995-04-12",
    "Bob": "2002-11-23",
    "Charlie": "1988-08-05",
}

youngest_name = None
youngest_date = None

for name, date_str in group.items():
    if youngest_date is None or date_str > youngest_date:
        youngest_name = name
        youngest_date = date_str

print(f"The youngest person is {youngest_name}, born on {youngest_date}.")

Make some changes #

1. Add two new members to the group:

- Frank, born on September 1st, 2011 ("2011-09-01")
- Grace, born on March 20th, 1975 ("1975-03-20")

2. Run the program. Check the result.
3. Now, we would like to find the oldest person instead of the youngest:
   1. Copy the program to a new file called find_oldest.py
   2. Modify the code so it finds and displays the oldest person in the group. Hints:
      1. Rename the variables from youngest_… to oldest_….
      2. Change the > operator to < in the if statement (an older birth date comes before in time, so it is smaller).
      3. Update the sentence in the print() statement in order to make sense. Run and check the result.

Making mistakes and obtaining errors is OK! It is the best and only way to learn. Be sure to read carefully errors thrown by the interpreter

Discussion #

See the Find the oldest person python program

On the usage of Gen. AI (LLMs) #

• Use it to :
  • Learn
  • Explain something (a concept, a copy/paste piece of code)
  • Debug some code
• Don’t use it to code/work for you ! Writing code has never been the problem
• You must be able to Understand, Explain and Modify your code without AI. You are responsible of your code and what it does.
• Make mistakes. In programming, you can test your understanding by executing your program! You will make mistakes and that’s ok. A (good) program is written iteratively.

Don’t worry, you will have PLENTY OF TIME to be productive in your (future) job! We are here to LEARN, not to be productive.

Learning Space vs Production Space #

• Learning space: Learn by making mistakes, Receive feedback, Do things manually, Use simple or specialized tools, Work on small-scale problems and systems, Follow provided specifications (labs, exams, projects)

• Production space: Gather requirements, specify a solution, Respect constraints (deadline, budget) and tradeoffs (quality/cost), Communicate, Use more complex environments and tools, Take responsibility, Deliver, Deploy to production, Monitor, Maintain, Work on large and complex systems

Next Module #

Go to next module

Going Further/Extra information #

About Von Neumann, the man from the future #

Von Neumann has made major contributions to quantum mechanics, functional analysis, mathematical logic, quantum logic, computer science, economics, etc! He also participated in U.S. military programs (Manhattan Project).

See The Man from the Future: The Visionary Life of John von Neumann, by Ananyo Bhattacharya, 2021, Allen Lane

Dynamic vs static languages #

The difference comes down to when variable types are checked: at compile time (before running) or at runtime (while running).

• Statically Typed languages:
  • Types are associated with variables and determined at compile time. Once a variable is declared as an integer, it cannot hold a string. Examples: C, C++, Java, Rust, Go, Swift.
  • Compilers can detect errors before running the program (at compile time)
• Dynamically Typed Languages :
  • Types are associated with values, not variables, and checked at runtime. A single variable can hold an integer, then a string, then a list, etc. Examples: Python, JavaScript, Ruby, PHP.
  • Faster to write, with less boilerplate code. Ideal for rapid prototyping.
  • Type errors cause crashes while the program is running!

Python IS a (strong) dynamically typed language

Demonstration: from high level code to binary code in C #

Compilation of a C program with gcc compiler.

1. High level C code (main.c)
2. After compilation (cc -S main.c), assembly code (main.s)
3. After assembling (cc main.c), binary code (a.out). See binary code in hexadecimal format with hexdump -C a.out

See full demo and documentation