Data Types, Variables, Operators, and Conditionals

In this page, we will explore the fundamental concepts of data types, variables, operators, and conditionals in Python.

🔢 Python Data Types¶

In programming, a data type is a classification that specifies which type of value a variable can hold. Let’s look at the most common basic data types in Python.

🔟 Integers (`int`)¶

Integers are whole numbers, both positive and negative, without any decimal points.

# An example of an integer
my_integer = 10
print(my_integer)
print(type(my_integer))

🌊 Floating-Point Numbers (`float`)¶

Floats are numbers that have a decimal point. They are used for representing real numbers.

# An example of a float
my_float = 3.14159
print(my_float)
print(type(my_float))

What are Complex Numbers?

Python also supports complex numbers, which are used in advanced mathematical computations.

Complex numbers are numbers that have both a real part and an imaginary part. They are often used in advanced mathematics, physics, and engineering. Python’s built-in complex type allows you to work with complex numbers easily.

For example, a complex number can be written as 3 + 4j, where 3 is the real part and 4j is the imaginary part. The j denotes the imaginary unit, which is the square root of -1.

z = 3 + 4j      # complex number
print(z)        # (3+4j)
print(z.real)   # 3.0
print(z.imag)   # 4.0

In this course, you will never encounter complex numbers.

🔤 Strings (`str`)¶

Strings are sequences of characters, used for storing text. You can create them by enclosing characters in either single quotes (') or double quotes (").

# An example of a string
my_string = "Hello, Python!"
print(my_string)
print(type(my_string))

✅ Booleans (`bool`)¶

Booleans represent one of two values: True or False. They are crucial for decision-making in programs.

# Examples of booleans
is_learning = True
is_difficult = False
print(is_learning)
print(type(is_difficult))

📦 Variables¶

A variable is a container for storing a value. You can think of it as a named label for a location in the computer’s memory. In Python, you create a variable by assigning a value to it using the equals sign (=).

In simple terms, a variable is simply a nickname for a stored value that can change.

❓ Why do we use variables?¶

If you have a value that changes often and is used in many different parts of a program, maintaining your code can become difficult—you would need to manually update every instance of that value. Instead, by creating a variable and referencing it, you only need to update the variable once, and every reference will use the updated value.

Variables also improve readability when used properly. For example, imagine you want to calculate the after-tax price (at a tax rate of 10%) of an item that costs 2 dollars. In Python, you could write this as 2 * 1.10. While you might understand what the numbers mean, others may find it confusing. Rewriting it as before_tax_price * (1 + tax_rate) makes your code much clearer and easier to read.

# Assigning values to variables
name = "Alice"
age = 30
height_meters = 1.7

print(name)
print(age)
print(height_meters)

You can change the value of a variable by reassigning it.

# Reassigning a variable
current_year = 2023
print("The current year is:", current_year)

current_year = 2024
print("The new year is:", current_year)

🆔 Variable Naming Rules¶

When naming variables in Python, you should follow these rules:

Variable names must start with a letter (a-z, A-Z) or an underscore (_).
The rest of the name can contain letters, numbers (0-9), or underscores.
Variable names are case-sensitive (myVar, MyVar, and MYVAR are different variables).
You cannot use Python reserved keywords (like if, else, while, etc.) as variable names.

# Example of valid variable names
first_name = "Alice"
age = 30
is_student = True

# Example of invalid variable names (uncommenting these will cause errors)
# 1st_name = "Alice"
# age@ = 30
# is student = True

Recommendations for Naming Variables:

Use descriptive names that convey the purpose of the variable (e.g., age, total_price, is_valid).
Use lowercase letters and separate words with underscores for better readability (e.g., first_name, total_amount).

For best practices, follow the PEP 8 style guide for naming conventions.

➕ Operators¶

Operators are special symbols that perform operations on variables and values.

📝 Assignment Operator¶

The assignment operator (=) is used to assign a value to a variable.

x = 5  # Assigns the value 5 to the variable x
y = 10 # Assigns the value 10 to the variable y

➗ Arithmetic Operators¶

These are used to perform mathematical operations.

+ : Addition
- : Subtraction
* : Multiplication
/ : Division
**: Exponent (Power)
% : Modulus (Remainder)

a = 10
b = 3

print("Addition:", a + b)
print("Division:", a / b)
print("Exponent:", a ** b)
print("Remainder:", a % b)

⚖️ Comparison Operators¶

These are used to compare two values and result in a boolean (True or False).

==: Equal to
!=: Not equal to
> : Greater than
< : Less than
>=: Greater than or equal to
<=: Less than or equal to

x = 5
y = 10

print("Is x equal to y?", x == y)
print("Is x less than y?", x < y)
print("Is y not equal to 10?", y != 10)

🔗 Logical Operators¶

These are used to combine conditional statements.

and: Returns True if both statements are true
or : Returns True if one of the statements is true
not: Reverses the result, returns False if the result is true

age = 25
has_ticket = True

# The person is old enough AND has a ticket
can_enter = (age >= 18) and (has_ticket == True)
print("Can enter the venue:", can_enter)

# Using 'not' to reverse the boolean
is_raining = False
print("Is it not raining?", not is_raining)

🔀 Conditionals (`if`, `elif`, `else`)¶

Conditionals allow your program to make decisions and execute different blocks of code based on whether a condition is true or false.

The structure is as follows:

if: The first condition to check.
elif: (short for “else if”) Optional. You can have as many of these as you need to check for other conditions.
else: Optional. This block of code runs if none of the preceding if or elif conditions are met.

temperature = 22

if temperature > 30:
  print("It's a hot day! Stay hydrated.")
elif temperature > 20:
  print("The weather is nice and warm.")
elif temperature > 10:
  print("It's a bit chilly, consider a jacket.")
else:
  print("It's cold outside. Bundle up!")

The elif and else blocks are optional

You can use just an if statement without elif or else if you only need to check one condition. Similarly, you can use if with else if you want to handle two scenarios (one for when the condition is true and another for when it is false).

🟢 Valid Example 1: Only if Statement

# The optional elif and else blocks are omitted
if city == "Urbana":
    print("Welcome to Urbana!")

🟢 Valid Example 2: Only if and else Statements

# The optional elif block is omitted
if chipotle.is_open():
    print("Let's get some burritos!")
else:
    print("Chipotle is closed. Let's try somewhere else.")

🔴 Invalid Example: elif without if

elif temperature > 20:
    # This will raise a SyntaxError because elif must follow an if statement
    print("The weather is nice and warm.")

📏 Indentation in Python¶

⚠️ Reminder: Unlike many programming languages that use braces {} or keywords to mark code blocks, Python uses indentation. This means that the amount of whitespace at the beginning of a line is significant and determines the structure of your code.

❗ Why Indentation Matters¶

Indentation groups lines of code together into blocks.
A block of code could be part of a function, a loop, a conditional, or a class.
All lines in the same block must be indented by the same amount.

If indentation is inconsistent, Python will raise an IndentationError.

🧩 Example: Conditional Block¶

x = 10

if x > 5:
    print("x is greater than 5")
    print("This line is also inside the if-block")

print("This line is outside the if-block")

Output:

x is greater than 5
This line is also inside the if-block
This line is outside the if-block

👍 Common Practices¶

Use 4 spaces for indentation (the Python standard).
Avoid mixing tabs and spaces. Python 3 does not allow it.
Most code editors (e.g., VS Code, PyCharm, Jupyter) can automatically insert 4 spaces when you press the Tab key.

In Python, indentation is not just style. It’s syntax. Correct indentation is required for your code to run.

Tools Used in This Course

Introduction to Python