Master Python Basics: From Code to Functions and Modules Explained

What is code? Code is a language that a computer can understand; unlike humans, a computer follows explicit instructions without ambiguity. Programming languages let us communicate with computers, and understanding this communication is key to reading code.

Programming = Algorithms + Data Structures

Python is a simple language with few keywords, used for all examples below.

1 Conditionals

Conditionals let the computer choose actions based on conditions using keywords like if, else, elif, and, or, and comparison operators.

if fruit_store_discount:
    buy_watermelon
else:
    do_not_buy

if fruit_store_discount:
    buy_watermelon
else:
    negotiate_with_owner
    if negotiation_successful:
        buy_watermelon
    else:
        do_not_buy

if fruit_store_discount:
    buy_watermelon
else:
    negotiate_with_owner
    if negotiation_successful and discount <= 5:
        buy_two_watermelons
    elif negotiation_successful and discount > 5:
        buy_one_watermelon
    else:
        do_not_buy

2 Loops

Loops repeat actions for multiple items using for, while, break, and continue.

for fruit_store in (Xianfeng, Siji, Street_stall):
    if fruit_store_discount:
        buy_watermelon
        break
    else:
        do_nothing
    bring_watermelon_home

3 Variables

Variables store values, acting as the computer’s memory. None represents an empty value. Assignment uses =, while == checks equality.

previous_max_discount = None
previous_best_store = None
for fruit_store in (Xianfeng, Siji, Street_stall):
    current_discount = owner_discount
    if current_discount < previous_max_discount:
        previous_max_discount = current_discount
        previous_best_store = fruit_store
buy_from(previous_best_store)

Variable Scope

A variable is only accessible within the block where it is first defined and any nested blocks.

previous_max_discount = None
previous_best_store = None
for fruit_store in stores:
    current_discount = get_discount()
    if current_discount < previous_max_discount:
        previous_max_discount = current_discount
        previous_best_store = fruit_store
buy_from(previous_best_store)

4 Functions

Functions group code into reusable blocks, improving readability and maintainability.

def buy_watermelon():
    for fruit_store in stores:
        if fruit_store_discount:
            buy_watermelon
        else:
            negotiate_with_owner
            if discount_successful:
                buy_two_watermelons
            elif discount_successful and discount > 5:
                buy_one_watermelon
            else:
                do_not_buy
buy_watermelon()
rest_one_day()
buy_watermelon()

4.1 Function Parameters

Parameters allow functions to operate on different data, such as buying various fruits.

def buy_fruit(fruit_name):
    for fruit_store in stores:
        if fruit_store_discount:
            buy[fruit_name]
        else:
            negotiate_with_owner
            if discount_successful:
                buy_two[fruit_name]
            elif discount_successful and discount > 5:
                buy_one[fruit_name]
            else:
                do_not_buy

buy_fruit('watermelon')
buy_fruit('pomelo')

5 Modules

Modules are files that contain functions, classes, and variables, allowing code to be organized and reused across projects.

# method 1
import a
a.buy_watermelon()
a.buy_banana()

# method 2
from a import *
buy_watermelon()
buy_banana()

# method 3
from a import buy_watermelon, buy_banana
buy_watermelon()
buy_banana()

6 Classes and Objects

Classes define the blueprint of objects, encapsulating state (attributes) and behavior (methods). Objects are instances of classes created at runtime.