Learn Python

Python is a high-level programming language, created by Guido van Rossum in 1991. But forget the boring theory: think of Python as a translator between you and the computer, but with such clear syntax that it feels like you're writing in English with simple rules.

Part 4: Loops

Objective: Repeat code without copying it.

for (when you know how many times)

for i in range(5): # 0,1,2,3,4
print(f"Turn {i+1}")

while (when you don't know when to stop)

answer = ""
while answer != "exit":
answer = input("Type 'exit' to finish: ")

Exercise: Write a program that adds numbers until the user enters 0 (and then displays the total sum).
Part 5: Lists and Dictionaries (day 6-8)

Objective: To store multiple data in an organized manner.

Lists (ordered sequence)

fruits = ["apple", "pear", "banana"]
fruits.append("orange") # Add
print(fruits[0]) # apple (starts at 0)
for fruit in fruits:
print(fruit)

Dictionaries (key → value)

student = {
"Name": "Luis",
"age": 20,
"city": "Bogotá"
}
print(student["name"])
student["email"] = "luis@mail.com" # Add new key
```✅ Exercise: Create a list of 3 dictionaries (each with the name and age of a friend). Go through it and show the name of the oldest.

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Part 6: Functions

Objective: To organize your code into reusable blocks.

```python
def calculate_tax(price, tax=21): # tax is optional (default 21)
return price (1 + VAT/100)

final_price = calculate_tax(100) # 121
final_price = calculate_tax(100, 10) # 110

Advantage: If you find a bug, you fix it only once (within the function) and it is fixed throughout the program.

✅ Exercise: Write a function is_older_than_age(age) that returns True or False. Use it in a program that asks for ages until the user enters -1.

Part 7: Files

Objective: To save data so that it is not lost when the program is closed.

# Keep
with open("notes.txt", "w") as file:
file.write("Python: 9\nMathematics: 7")

Part 0:

Objective: To have everything ready to write code.

1. Download Python from python.org (check "Add to PATH" during installation).
2. Install VS Code and add the "Python" extension (the one from Microsoft).
3. Create a folder my_projects and inside it a file hello.py.
4. Type print("Hello, world") and click "Run" (triangle at the top right).

✅ Exercise: Change the text to your name and run it 3 times with different messages.

Part 1: Variables and Data Types

Objective: To save information in the computer's memory.

name = "Ana" # Text (str)
age = 25 # Integer (int)
height = 1.65 # Decimal number (float)
is_student = True # True/False (bool)

Golden rule: Python guesses the type automatically, but you can't mix without converting:

· "I have " + str(age) + " years" → you convert number to text.
· int("10") + 5 → converts text to number.

✅ Exercise: Create variables with your city, year of birth, and whether you like ice cream. Then display a phrase like: "I live in Madrid, I was born in 2000, and I like ice cream: True."

Part 2: Entrance and Exit

Objective: For the program to talk to you (and you to it).

name = input("What's your name?")
age = int(input("How old are you? ")) # Note! input always returns text
print(f"Hello {name}, next year you will be {age + 1} years old")Tip: f-strings (with the f in front) are the cleanest way to mix text and variables.

✅ Exercise: Ask for the price of a product and the discount percentage, and display the final price.

Learn how to execute your first print("Hello, world").

2. Essential Fundamentals (the 80% you use 80% of the time)

· Variables and Types: int, float, str, bool.
• Input/Output: input() and print() with f-strings (f"Hello {name}").
· Conditionals: if, elif, else.
· Loops: for (for iterating) and while (for conditions).
• Data structures: Lists (mutable), Tuples (immutable), Dictionaries (key-value) and Sets (no duplicates).
· Functions: def my_function(param): and the concept of return.

3. Common Mistakes (so you don't get frustrated)

· IndentationError: Python is sensitive to indentation (always use 4 spaces).
· NameError: You misspelled a variable.
· TypeError: You added text to a number (convert with int() or str()).

4. Next Steps (when you master the basics)

• File handling: open() to read/write .txt.
· Exceptions: try/except to prevent your program from crashing.
• List comprehension: [x2 for x in range(5)] (cleaner code).
· Lambda functions and string methods (.split(), .join()).