5. Data Types

Data Types classify the kind of information a variable stores. Knowing the data type is essential, as it defines which operations (mathematical, logical, or text manipulation) can be performed with that value.

Understanding the difference between the basic types is critical for program's logic and memory management, ensuring operations run accurately and efficiently.

1. Primitive Categories and Casting

1.1. Primitive Categories

In Python, the most common primitive data types are grouped into numbers(integers and floats), sequences (strings), and logical values (booleans). These types are the building blocks of any program.

Data Type	Python Name	Description	Example Assignment
Integer	int	Whole numbers, positive or negative, without decimals.	age = 25
Floating-point	float	Numbers that contain a decimal point.	price = 99.99
String	str	Sequences of characters (text). Must be enclosed in single or double quotes.	name = "Ana"
Boolean	bool	Logical values that can only be True or False.	is_active = True

Note that Python also includes more complex data structures for organizing collections of data (like lists, tuples, and dictionaries).

1.2. Type Casting

When working with different data types, there are strict rules about how they combine and when conversion is necessary (a process called Type Casting).

1.2.1. Input Conversion (input())

The input() function always returns user data as a string (str). If mathematical calculations are required, conversion using int() or float() is mandatory:

# User input (always str)
str_value = input("Enter your age: ")

# Conversion is necessary to perform mathematical operations
int_value = int(str_value)

# Now you can calculate future age:
future_age = int_value + 10
print("Your age in 10 years will be:", future_age)

1.2.2. Automatic Promotion to float

If an integer (int) is combined with a floating-point number (float) in an arithmetic operation, Python automatically converts the result to a float type to ensure decimal precision is not lost.

integer_value = 10    # int
float_value = 0.5     # float

# The result will be a float (10.5)
result = integer_value + float_value

print(type(result))
# Output: <class 'float'>

2. Commented Examples

2.1. Demonstrating Type Casting

# 1. Input: Prompt user for age (receives str data)
age_str = input("Please enter your age: ") 

# 2. Process: Convert the str input to an integer (int) for math
age_int = int(age_str) 

# 3. Process: Add 1 to age
age_next_year = age_int + 1 

# 4. Process: Convert the integer result back to str for display
message = "Your age next year will be: " + str(age_next_year)

# 5. Output: Display the message
print(message) # Example Output: Your age next year will be: 21

Explanation:

• input() always returns a string (str).
• Type Casting (int()) is required for arithmetic operations.
• The str() function converts numeric types back to text for display.

2.2. Mixing Types (Float Promotion)

# 1. Setup: Define an integer variable (int)
a = 5

# 2. Setup: Define a floating-point variable (float)
b = 2.5

# 3. Process: Perform the operation (Python promotes the result to float)
result_float = a - b

# 4. Output: Display the result and verify the resulting data type
print(result_float)   # Output: 2.5
print(type(result_float)) # Output: <class 'float'>

Explanation:

• When an operation mixes int and float, the result is promoted to float.
• This rule ensures that decimal precision is preserved.
• The float type represents non-whole numbers.

3. Short Practice Exercises

3.1. Type Prediction

What is the final data type of the variable result after this calculation?

num_int = 5
num_float = 2.0
result = num_int + num_float

Show solution

float

Explanation: 5 + 2.0 = 7.0

3.2. Conversion Requirement

How should the code be corrected so that the final result of the addition is 30?

value_a = "20"
value_b = 10
result = value_a + value_b

Show solution

value_a = "20"
value_b = 10
result = int(value_a) + value_b
# result is 30 (int)

Explanation: The string must be converted to an integer:

3.3. Boolean vs. String

What is the data type stored in the variable status?

status = "False"

Show solution

str (String).

Explanation: The quotes around "False" make it text data, not a logical boolean value.

3.4. Correcting a Type Error

The following code produces an error. What code line should be added to fix it?

age = input("Enter your age: ")
future_age = age + 5
print(future_age)

Show solution

age = int(age)

Explanation: input() returns a string, so converting age to int allows adding 5 without a TypeError.

4. Google Colab: Try It Yourself

Practice recognizing data types and applying type casting with this Colab notebook:

👉 Open the Data Types Colab notebook ↗

First time using Google Colab? Read the quick beginner guide ↗

5. Mini-Quiz

5.1. Which Python function always returns the user's input data as a String type?

A) print()
B) int()
C) input()
D) float()

Show answer

C) input()

5.2. What data type is stored in the variable count after the following line?

count = 12 / 4

A) Integer (int)
B) String (str)
C) Boolean (bool)
D) Float (float)

Show answer

D) Float (float)

5.3. If user_age was obtained using input(), which conversion is necessary to perform the operation 2 * (user_age)?

A) user_age = str(user_age)
B) user_age = float(user_age)
C) user_age = int(user_age)
D) No conversion is required

Show answer

C) user_age = int(user_age)

5.4. Which of the following is a boolean data type?

A) True
B) 1.23
C) "True"
D) 123

Show answer

A) True

5.5. Which data type is used to store a value like "Hello World"?

A) Integer
B) Float
C) Boolean
D) String

Show answer

D) String

6. Common Mistakes

• Forgetting to convert input values with int() or float() before using them in calculations.
• Trying to combine a string and a number with + (e.g., "age: " + 18).
• Writing Boolean values as strings ("True" / "False") instead of actual booleans.
• Using lowercase true or false, which Python treats as undefined variables.

7. Summary Diagram

mindmap
  root((Data Types))
    Numeric Types
      Integer (int)
      Float (float)
    Text Type
      String (str)
    Logical Type
      Boolean (bool)
    Conversion (Type Casting)
      int
      float
      str

8. Optional Extensions

• Write a short program with input() and conversions (int() vs. float()).
• Explore the additional data types beyond primitives (list, tuple, dict).
• Research the difference between mutable and immutable data types.