46. Mid-Way Mental Map

1.2 CORE BASICS

Everything is an object. Know your containers.

The "Big Four" Collections

Structure	Syntax	Mutable?	Ordered?	Best Used For...
List	x = [1, 2, "a"]	Yes	Yes	General sequences, updating items.
Tuple	x = (1, 2, "a")	No	Yes	Fixed records, dictionary keys.
Set	x = {1, 2, "a"}	Yes	No	Removing duplicates, math logic (union/intersection).
Dict	x = {"k": "v"}	Yes	Yes	Lookups, mapping keys to values, structured data[cite: 379, 384].

Essential Operations

• Strings: Use f-strings for formatting: f"Hello {name}". Use raw strings for paths: r"C:\path\to\file".
• Slicing: sequence[start:stop:step]. Example: my_list[::-1] reverses a list.
• Type Casting: int("5"), str(42), list((1, 2, 3)).
• Booleans & Logic: Falsy values include 0, "", [], {}, None, and False. Everything else evaluates to True. Combine with and, or, not.

1.3: CONTROL FLOW

Directing the traffic of your program.

Conditionals

Check conditions from most specific to least specific. Python checks conditions top to bottom.

if score >= 90:
    print("A")
elif score >= 80:     # Only checked if the 'if' is False
    print("B")
else:                 # Catch-all
    print("Study harder!")

Loops

• for loops: Used when the number of iterations is known (iterating over lists, strings, range())[cite: 447, 448].
• while loops: Used when iterations depend on a condition remaining True. Watch out for infinite loops!
• Loop Control:
  • break: Exits the innermost loop entirely[cite: 468, 470].
  • continue: Skips the rest of the current iteration and moves to the next[cite: 468, 471].
  • pass: Does absolutely nothing (acts as a structural placeholder)[cite: 469, 473].

Comprehensions

The Pythonic, readable way to create collections from existing iterables.

# [expression for item in iterable if condition]
evens = [x for x in range(10) if x % 2 == 0]

1.4 FUNCTIONS, SCOPE & ENVIRONMENT

Building reusable, modular, and isolated code.

Anatomy of a Function

def process_data(required_arg, default_arg="Hello", *args, **kwargs):
    """Docstring: Explains what the function does."""
    # *args collects extra positional arguments into a TUPLE.
    # **kwargs collects extra keyword arguments into a DICT.
    return result

Scope Resolution (LEGB Rule)

Python checks for variables in this order:

1. Local: Inside the current function.
2. Enclosing: Inside any enclosing (nested) functions.
3. Global: Defined at the top level of the script. (Use the global keyword to modify these inside a function ).
4. Built-in: Python's reserved names (like len or print).

Modules & Environments

• Importing: import my_module or from my_module import my_func[cite: 535, 536]. Keep your custom modules focused and small.
• Virtual Environments (venv): Project-specific sandboxes for your dependencies so you don't break your global Python installation.
  • Create: python3 -m venv venv
  • Activate (Linux/Mac): source venv/bin/activate
• Package Management (pip):
  • Save state: pip freeze > requirements.txt
  • Install state: pip install -r requirements.txt