Python Reference -- PAGE UNDER CONSTRUCTION --

Python & Programming Concepts

Created by Guido van Rossum (Netherlands, 1991), Python's syntax mirrors the English language, letting developers accomplish more with fewer lines of code. It runs cross-platform on Windows, Mac, and Linux.

Python is an interpreted (scripting) language — the interpreter executes code line-by-line at run-time, unlike compiled languages that translate the entire program before execution.

Automate the Boring Stuff Setup Guide Official Docs

Variables

Named containers for storing and referencing data values in a program.

§ 01

In Python, a variable is created at the moment you first assign a value — no explicit declaration needed. Variables are dynamically typed and can change type after being set.

variables.py

x = 5
y = "John"

# Multiple assignment
x, y, z = "Orange", "Banana", "Cherry"
a = b = c = "Orange"

# Global keyword inside function
count = 0
def increment():
    global count
    count += 1

Created on first assignment — no declaration command
Dynamically typed; type can change at any time
Cannot begin with a number — only letters or underscore
Case-sensitive: age, Age, and AGE are three distinct variables
Alphanumeric + underscore only; no hyphens or spaces
String and int cannot be concatenated directly with +
Use global keyword to modify global variable inside a function

W3Schools — Python Variables

JavaScript

variables.js

var   a = 27;
let   b = "hello";
const PI = 3.14;

Use var, let, or const. Values in quotes. End statements with semicolon. Prefer const/let over var in modern JS.

PHP

variables.php

$name  = "Alice";
$score = 42;

All variables must begin with $. Semicolons required. No type declaration needed.

Input and Output

Reading data from the user and displaying results — a program's primary communication channel.

§ 02

Python

io_example.py

name = input("Enter your name: ")
print("Welcome,", name)
print(f"Hello, {name}!")  # f-string

JavaScript	PHP
`name = prompt("Your name?")`	Use `$_POST` or `$_GET` superglobals for form input
`alert("Hello, " + name)` `console.log(name)`	`echo "Hello " . $name;` `print("Hello");`

Strings

Ordered sequences of characters enclosed in quotes. The most common data type in web programming.

§ 03

In Python, strings are arrays of characters — you can index and slice them. An escape character is a backslash \ followed by the intended character.

strings.py

a = "Hello, World!"
print(a[1])          # → 'e'
print(a[0:5])       # → 'Hello' (slice)
print(len(a))       # → 13
print(a.upper())    # → 'HELLO, WORLD!'

# Escape characters
b = "She said \"hi\""
c = "Line1\nLine2"   # \n = newline

Strings are arrays — access via index: a[0]
Slicing: a[start:end] — end index is exclusive
Escape with backslash: \" \' \n \t

W3Schools — Python Strings ↗

JavaScript	PHP
`document.write("Hi " + aName);`	`$s = "this is a string";`
Template literals: `Hello ${name}`	Concatenate with `.` (dot): `"Hi " . $name`
`"text".length`	`strlen($s)`

Arrays & Collections

Python provides four built-in collection types — each suited to different data-storage needs.

§ 04

Array syntax: list_name = [item1, item2, ...] — e.g. cars = ["Saab", "Volvo", "BMW"]

JavaScript

arrays.js

// Array literal (preferred)
const names = ["Sam", "Jo"];
// Constructor syntax
var arr = new Array(2);
arr[0] = "Sam";

PHP

arrays.php

// Indexed array
$cars = ["Saab", "Volvo", "BMW"];
// Associative (key→value)
$ages = ["Alice" => 25];

PHP's powerful associative arrays work like Python dictionaries, with many built-in functions.

list

List

General-purpose ordered collection. The Python equivalent of an array.

Ordered Changeable Duplicates ✓

x = ["apple", "banana", "cherry"] cars = ["Saab", "Volvo", "BMW"] x.append("date") # add item x.remove("apple") # remove item

Use square brackets [ ]

tuple

Tuples

Immutable ordered collection. Faster iteration than lists; can be used as dictionary keys.

Ordered Immutable Duplicates ✓

tup1 = ('physics', 'bio', 2000) tup2 = (1, 2, 3) tup3 = (50,) # single item needs comma tup4 = () # empty tuple

Use round brackets ( )

set

Sets

Unordered, unindexed. Ideal for membership testing and removing duplicates.

Unordered No Duplicates

fruits = {'apple', 'banana', 'cherry'} print("apple" in fruits) # True fruits.add("date") # add one fruits.update(["fig"]) # add many for x in fruits: print(x)

Use curly brackets { }

dict

Dictionaries

Key-value store. Keys must be unique and immutable; values are freely changeable.

Key:Value Changeable No Dup Keys

purse = {} purse['money'] = 10 purse['candy'] = 'pink' # Inline syntax: d = {'key': 'value', 'n': 42} d['key'] = 'updated' # change value

Syntax: {key: value, ...}

Conditional Statements — if | else

Control structures alter the flow of execution. Flavours: if, if|else, if|elif|else.

§ 05

if_else.py

# if | else
num = 3
if num >= 0:
    print("Positive or Zero")
else:
    print("Negative number")

if_elif_else.py

# if | elif | else
num = 3
if num > 0:
    print("Positive number")
elif num == 0:
    print("Zero")
else:
    print("Negative number")

JavaScript & PHP: Conditional syntax is nearly identical in both — curly-brace blocks: if (expr) { ... } else if (expr) { ... } else { ... }

Loops & Iterations

while — indefinite, runs until condition is false. for — definite, iterates a sequence.

§ 06

while_loop.py

# Syntax
while <expression>:
    <statements>

# Example
i = 0
while i < 5:
    print(i)
    i += 1

for_loop.py

# Syntax
for <variable> in <iterable>:
    <statements>

# Example
fruits = ["apple", "banana"]
for f in fruits:
    print(f)

# Range-based
for i in range(5):
    print(i)

JavaScript

Supports for, while, do...while, for...of (arrays), and for...in (object keys).

PHP

Loop syntax mirrors JavaScript: for ($i=0; $i<5; $i++) and foreach ($arr as $key => $val) for arrays.

Functions

Reusable named blocks of code. Define once, call anywhere. Reduces duplication.

§ 07

functions.py

# Define with def keyword
def greet(name):
    print(name + " Roger")

greet("Mat")   # → "Mat Roger"

# With return value
def add(a, b):
    return a + b

result = add(3, 4)  # → 7

JavaScript

functions.js

// Declaration
function greet(name) {
    console.log("Hello, " + name);
}
// Arrow function (ES6)
const add = (a, b) => a + b;

PHP

functions.php

function greet($name) {
    echo "Hello, " . $name;
}
greet("Alice");

Operators

Symbols that perform operations on variables and values.

§ 08

Operator	Name	Description	Python Example
`**`	Exponent	Raise left to the power of right	`2 ** 8` → 256
`+ - * /`	Arithmetic	Standard mathematical operations	`a + b`
`%`	Modulus	Remainder after division	`10 % 3` → 1
`//`	Floor Division	Division rounded down to nearest integer	`9 // 2` → 4
`== != < > <= >=`	Comparison	Compare two values; returns boolean	`x == y`
`and or not`	Logical	Combine or negate boolean expressions	`x > 0 and x < 10`
`= += -= *=`	Assignment	Assign or update a variable's value	`x += 5`
`in not in`	Membership	Test if value exists in sequence	`"a" in ["a","b"]`
`is is not`	Identity	Compare object identity (memory address)	`x is None`

Environment Setup & IDEs

Tools and resources to get your Python development environment running.

§ 09

IDE Options

An IDE (Integrated Development Environment) combines a code editor, debugger, and build tools in one application.

PyCharm — Full-featured Python IDE (JetBrains)
VS Code — Lightweight, highly extensible, most popular
Atom — Open-source hackable editor (GitHub)
Eclipse — Java-based, multi-language with PyDev plugin
Repl.it — Free web-based IDE — no installation needed

Setup Python Environment Tutorial

Flowchart & Diagram Tools

Visualise algorithms and pseudocode before writing a single line of code.

Tip: Sketching the logic as a flowchart first dramatically reduces debugging time for complex programs.