Python Fundamentals and Algorithms Explained

Algorithms

Algorithms involve inputs, instructions, outputs, and a purpose.

Instruction Types

• Instruction
• Decision
• Loop
• Variable
• Function

Python Basics

Comments

Comments explain what code is for, intended for human readers.

Variables

Storing a value in a variable is called assignment. It's best practice not to use generic names.

Calculations (Operators)

• + : Addition
• - : Subtraction
• * : Multiplication
• / : Division
• // : Integer Division (e.g., 6 // 4 = 1)
• % : Remainder / Modulo (e.g., 6 % 4 = 2)
• ** : Exponentiation

mass_in_kg = 15

weight_in_pounds = mass_in_kg * 2.2

print('the weight in pounds is: ', weight_in_pounds)

user_name = input("enter your user name: ")

print('hello', user_name)

Data Types

• int: Integer numbers (e.g., -1, 0, 2, 1000)
• float: Floating-point (real) numbers (e.g., 3.14159, 2.0)
• str: A text string (e.g., 'A', 'Hello World!'). Anything enclosed by single or double quotes.
• bool: Boolean logic values (True, False).

When mixing int and float types in calculations, the outcome is only an int if both operands are int.

gas_price = float(input('enter the price of gas: '))

Strings

String Concepts

• Values that never change are called constants (often written in uppercase).
• str: A text string (e.g., 'A', 'Hello World!'). Anything enclosed by single or double quotes.

String Concatenation and Input

first = input('Enter your first name: ')

last = input('Ok ' + first + ', now enter your last name: ')

print('hi ' + first + ' ' + last)

Escape Characters

• \n: New line
• \t: Tab

F-Strings (Formatted String Literals)

Easily insert a variable's value into a string.

first_name = 'Willy'

last_name = 'Wonka'

print(f'hi {first_name} {last_name}')

Format Specifiers

Used within f-strings or .format().

• :.2f: Format as a floating-point number with 2 decimal places.
• :%: Format as a percentage.
• :10.2f: Format as a floating-point number with 2 decimal places, right-aligned in a field 10 characters wide.

General format: [alignment][width][,][.precision][type]

String Methods

• 'hello'.upper(): Returns the uppercase version ('HELLO').
• 'hello'.lower(): Returns the lowercase version ('hello').

Functions

A group of instructions that can be grouped together and referred to as a whole. Functions can have inputs (arguments/parameters) and can produce/return outputs.

Types of Functions

• Value-Returning Functions: Produce or return some output (something new).
  Example: user_name = input('enter name: ')
• Void Functions (Subroutines): Don't return anything explicitly (often perform an action like printing).
  Example: print('hello')

Function Definition Syntax

def function_name(parameter1: type1, parameter2: type2, ...) -> return_type:

    # Instructions that use parameters

    return something # Optional, for value-returning functions

Void Function Example

def greeting(name: str) -> None:

    print(f'Hello {name}')

user_name = input('enter your name: ')

greeting(user_name) # Calling the function with an argument

Value-Returning Function Example

def add_two_integers(x: int, y: int) -> int:

    the_sum = x + y

    return the_sum

sum = add_two_integers(2, 3) # Calling the function and storing the returned value

print(sum)

Variable Scope (Local vs. Global)

• Local Variables: Defined inside a function and only accessible within that function.
• Global Variables: Defined in the main program body and accessible from anywhere (including inside functions, though modifying them requires the global keyword).

Another Function Example (Corrected Syntax)

def add_2_numbers(x: float, y: float) -> None: # Parameters: x, y

    sum_result = x + y # Local variable: sum_result

    print(sum_result) # Function body

add_2_numbers(2.1, 3.8) # Arguments: 2.1, 3.8