🎯 Learning Objectives
By the end of this module, students will be able to:
Understand what variables are and how to use them.
Identify and apply different data types.
Perform type conversions (casting).
Avoid common variable naming mistakes.
🧠 1. What is a Variable?
A variable is a name that refers to a value stored in memory.
Think of it as a label on a box that stores a piece of data.
name holds "Alice", age holds 20.
🗂️ 2. Python Data Types
Data Type Example Description int25Whole numbers float3.14Decimal numbers str"Hi"Text values boolTrueLogical values (True/False)
Example:
x = 10 # int
y = 3.5 # float
name = "Sam" # str
flag = True # bool
📝 3. Variable Naming Rules
✅ Valid Names:
Must begin with a letter or _
Can contain letters, digits, and underscores
Case-sensitive (name ≠ Name)
Example :
# 2name = "Alex" ❌ starts with number
# user-name = "Bob" ❌ contains dash
# my name = "Joe" ❌ contains space
🔄 4. Type Conversion (Casting)
age = "20" # str
nextyearage=age+1
#TypeError: can only concatenate str (not "int") to str
nextyearage=int(age)+1
print (nextyearage) # 21
Use int(), float(), str(), bool() for conversions.
🧪 5. Checking Data Types
use type() function
print(type(10)) # <class 'int'>
print(type("hello")) # <class 'str'>
⚠️ 6. Common Mistakes
Mistake Why it’s wrong Fix "age" + 5Can’t add string and integer Convert first: int("age") + 5 user name = "Tom"Variable names can’t have spaces Use underscore: user_name
🧩 7. Practice Time (Live Demo)
Create a variable city and assign your city name.
Create variables for your birth year and calculate your age.
Convert a float to a string and print the result and type.
Check if bool(0) and bool("Hi") return True or False.
📚 Quick Recap
Variables hold data values.
Data types define the kind of value.
Use type() to inspect types.
Convert types using casting functions like int(), str().
Follow naming rules for valid variables.
Example 1:
name = "John"
age = 28
height = 5.9
print(name)
print(age)
print(height)
Output
Example 2: Check Data Type
print(type(name)) # str
print(type(age)) # int
print(type(height)) # float
Output
<class 'str'>
<class 'int'>
<class 'float'>
Example 3: Type Casting
age = 28
height = 5.9
age = float(age)
height = str(height)
print(age)
print(type(age))
print(height)
print(type(height))
Output
28.0
<class 'float'>
5.9
<class 'str'>
Example 4: Assign multiple values in one line.
a, b, c = 1, 2, 3
print(a, b, c)
Output
Example 5: Assign Same Value to Multiple Variables
x = y = z = "Python"
print(x, y, z)
Output
Example 6: String Concatenation using Variables
first = "Hello"
last = "World"
message = first + " " + last
print(message)
Output
Example 7: Numeric Calculation Using Variables
price = 50
quantity = 3
total = price * quantity
print("Total:", total)
Output
Example 8: Boolean Example
is_logged_in = True
print("Login status:", is_logged_in)
Output
Example 9: Dynamic Typing in Python
var = 10
print(type(var)) # int
var = "Ten"
print(type(var)) # str
Output
<class 'int'>
<class 'str'>
Example 10: Input and Type Conversion
name = input("Enter your name: ")
age = int(input("Enter your age: "))
print(f"Hello {name}, you are {age} years old.")
Output
Enter your name: Alex
Enter your age: 21
Hello Alex, you are 21 years old.
Example 11: Using type() in Debugging
value = "123"
print(value + " is a string") # works
# print(value + 5) # ❌ TypeError
value = int(value)
print(value + 5) # ✅ Now works
Output
Example 12: Calculate the Area of a Rectangle
length = 10
width = 5
area = length * width
print("Area of rectangle:", area)
Output
Example 13: Store and Display Product Info
product_name = "Laptop"
price = 799.99
in_stock = True
print("Product:", product_name)
print("Price: $", price)
print("Available:", in_stock)
Output
Product: Laptop
Price: $ 799.99
Available: True
Example 14: Temperature Storage in Celsius and Fahrenheit
celsius = 25
fahrenheit = (celsius * 9/5) + 32
print("Celsius:", celsius)
print("Fahrenheit:", fahrenheit)
Output
Celsius: 25
Fahrenheit: 77.0
Example 15: Using Variables to Format Strings
name = "Sara"
score = 95
print(f"{name} scored {score} points.")
Output
Example 16: Variable Reassignment
x = 10
print("Before:", x)
x = 20
print("After:", x)
Output
Example 17: Using bool() Function
print(bool(0)) # False
print(bool(123)) # True
print(bool("")) # False
print(bool("Hi")) # True
Output
Example 18: Type Conversion with Errors (Demonstration)
x = "ten"
# y = int(x) # This will cause an error
print("Cannot convert non-numeric string to integer")
Output
Cannot convert non-numeric string to integer
Example 19: Combining Strings and Numbers with Casting
name = "Liam"
score = 88
print(name + " scored " + str(score) + " marks.")
Output
Example 20: Constants (Using UPPERCASE by Convention)
PI = 3.14159
radius = 7
area = PI * radius * radius
print("Circle Area:", round(area, 2))
Output
Welcome to the Python Programming Quiz!
Test your knowledge by selecting the correct answers. You will immediately see if you’re right or wrong.
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