Python Variables and Data Types

Learning Objectives

• Intended outcomes include understanding of variables and their storage, Python data types, working with a Budget & Expense Tracker, learning about lists, and completing a Sales Transactions exercise.

Variables

• A variable is a name representing a value in computer memory.
• Variables access and change data in memory.
• Variables store a reference to a value.
• Assignment statements create variables and assign values, using the format variable_name = expression.
• The assignment operator (=) assigns the right side value to the variable on the left.
• For example, in age = 29, age is the variable, = is the operator, and 29 is the assigned value.

Variable Assignment Example

• Assigning x = 5 associates the name x with the integer value 5, while y = 5.0 assigns the floating-point value 5.0 to y.
• Python allows reassigning a variable to a different data type.
• For example x can be first assigned an integer (e.g., x = 5), and later reassigned to a string value (e.g., x = "Hello").

Variable Arithmetic Example

• Variables can be used within arithmetic statement
• For example;
• price = 50
• discount = 10
• final_price = price - discount
• print("Final Price:", final_price) would result in a final price of 40

Variable Naming Rules

• Variable names must start with a letter (A-Z or a-z) or an underscore (_).
• _myVariable, x_value, and name1 are valid.
• 1name and @value are invalid.
• Variable names cannot start with a number.
• var1 and x_y are valid.
• 5data and 9score are invalid.
• Variable names can include letters, digits, and underscores.
• my_variable, score99, and _temp_value are valid.
• my-variable, first name, and data@home are invalid.
• Reserved words in Python cannot be used as variable names.
• _def = 10 and if_value = 5 are valid.
• def = 10 and if = 5 are invalid.
• Variable names are case-sensitive
• Meaning name, Name, and NAME are distinct variables.

Data Types

• Data types classify data items, determining the operations that can be performed on data.
• Python treats everything as an object, where data types are classes and variables are instances of these classes.

Python Data Types

• Numeric: Represents numeric values as integers (int), floating-point numbers (float), or complex numbers (complex).
• Boolean: Represents True or False values (bool).
• String: Represents a sequence of characters (str).
• List: Holds an ordered collection of items (list).
• Tuple: Holds an ordered, immutable collection of items (tuple).
• Set: Holds an unordered collection of unique items (set, frozenset).
• Dictionary: Holds data in key-value pairs (dict).

Data Type Examples

• Integers are whole numbers, either positive or negative (e.g., x = 5).
• Floating-point numbers have decimal points (e.g., Salary = 2568.50).
• Strings are sequences of characters enclosed in single or double quotes (e.g., name = “Bella”).

Type Function

• The type() function determines the data type of a variable.

Budget & Expense Tracker Exercise

• Write script to manage a company's budget, including storing the company name (string).
• Track the total budget (float), monthly rent, salary, and marketing expenses (floats).
• Calculate the remaining budget and display all details in a clear format.

Lists in Python

• Lists are collections holding items of any data type, including other lists.
• Lists are fundamental containers in Python, which can hold numbers, words.
• You can add as many items as you want.
• Lists are mutable, allowing changes after creation, are enclosed in square brackets [], items are separated by commas.

Creating and Using a List

• An empty list is created using mylist = [].
• Items are added using the append() method (e.g., mylist.append(1)).
• Elements are accessed by their index, starting from zero.
• print(mylist[0]) returns the first item in the list

Business Revenue Example

• Lists can store revenue from different business locations for example, branch_revenue = [10500, 13200, 8900, 15600, 9800].
• Values can be accessed for example print("Revenue of second branch: $", branch_revenue[1]).

Shopping Cart with Discount Exercise

• Task is to implement an algorithm to calculate the total price of the shopping cart after applying a discount.
• Follow the following order
• Start step one
• Input the total price of items in the cart
• Input the discount percentage
• Use the formula Discount Amount = (Total Price × Discount Percentage) / 100
• Then use formula Final Price = Total Price − Discount Amount
• Display the final price after completing steps.

Lists with Multiple Distinct or Duplicate Elements

• Lists can contain duplicate values, retaining each value's position.
• For example numbers = [10, 20, 30, 10, 40, 50, 20]
• Printing will return ("List with duplicate values:", numbers)
• The returned list will have all duplicates e.g., [10, 20, 30, 10, 40, 50, 20].

Accessing List Elements

• List items are accessed by their index number.
• Index operator [] accesses an item in a list.
• The index must be an integer.
• Nested lists use nested indexing.

Analysing Sales Transactions Exercise

• A list can represent daily sales transactions, with sale amounts in dollars.
• Create a list called sales containing the following sales amounts: [150, 200, 350, 150, 500, 300, 200, 150, 150].
• Print the list with the print() keyword.
• Count occurrences of $150 using the sales.count() function.
• Calculate total revenue by summing all sales.

String Concatenation

• Python concatenates strings and supports simultaneous variable assignment.
• Strings are concatenated using the + operator.
• one = 1, two = 2, three = one + two will outputs 3
• "hello" + "world" yields "hello world"

Simultaneous Variable Assignment

• Multiple variables can be assigned values in a single line using a tuple-like syntax.
• This enables concise and readable code.
• For example, x, y = 10, 20 assigns 10 to x and 20 to y in one line.

Mixing Operators

• It isn't a good idea to use the same operator for number and strings

Indentation

• Python relies on indentation to define code blocks.
• It is fundamentally helps with code structure and readability.
• Indentation is adding whitespace before a statement within a code block.
• Always use spaces OR tabs for indentation, never use both.
• Use 4 spaces as convention

Indentation and Code Structure

• Indentation determines code structure.
• Statements with equal spacing belong to to the same block of code .
• Common blocks requiring indentation include loops, conditional statement, functions and lass definitions.
• An if statement example would be;
• temperature = 30
• if temperature > 25:
• print("It's a warm day.")