Variables & Data Types

What Are Variables?

A variable is a name that refers to a value stored in memory. In Python, you create a variable simply by assigning a value to a name using the = operator. Unlike languages like Java or C++, you don't need to declare the type — Python figures it out automatically.

variables.py

1# Creating variables
2name = "Skill-Forge"
3age = 21
4pi = 3.14159
5is_active = True
6 
7print(name)      # Skill-Forge
8print(type(age)) # <class 'int'>

Output

Skill-Forge
<class 'int'>

Core Data Types

Python has several built-in data types. The most commonly used are: int (whole numbers), float (decimal numbers), str (text), bool (True/False), and NoneType (represents absence of a value). Each type has its own set of operations and methods.

data_types.py

1# Integer
2count = 42
3 
4# Float
5temperature = 36.6
6 
7# String
8greeting = "Hello, World!"
9 
10# Boolean
11is_student = True
12 
13# NoneType
14result = None
15 
16# Check types
17print(type(count))       # <class 'int'>
18print(type(temperature)) # <class 'float'>
19print(type(greeting))    # <class 'str'>

Output

<class 'int'>
<class 'float'>
<class 'str'>

Variable Naming Rules

Variable names must start with a letter or underscore. They can contain letters, digits, and underscores. Python is case-sensitive: age, Age, and AGE are three different variables. By convention, use snake_case for variable names (e.g., user_name, total_count).

naming.py

1# Valid names
2user_name = "Alice"
3_private = 42
4totalCount2 = 100
5 
6# Invalid names (will cause errors)
7# 2nd_place = "Bob"   # Can't start with digit
8# my-var = 10         # Hyphens not allowed
9# class = "Math"      # Reserved keyword

Type Conversion

You can convert between types using built-in functions: int(), float(), str(), bool(). This is called type casting. Be careful — not all conversions are valid (e.g., converting "hello" to int will raise a ValueError).

type_conversion.py

1# String to Integer
2age_str = "25"
3age_num = int(age_str)
4print(age_num + 5)  # 30
5 
6# Integer to String
7count = 42
8message = "Items: " + str(count)
9print(message)  # Items: 42
10 
11# Float to Integer (truncates)
12pi = 3.99
13print(int(pi))  # 3

Output

30
Items: 42
3

What Are Variables?

variables.py

1# Creating variables
2name = "Skill-Forge"
3age = 21
4pi = 3.14159
5is_active = True
6 
7print(name)      # Skill-Forge
8print(type(age)) # <class 'int'>

Output

Skill-Forge
<class 'int'>

Core Data Types

data_types.py

1# Integer
2count = 42
3 
4# Float
5temperature = 36.6
6 
7# String
8greeting = "Hello, World!"
9 
10# Boolean
11is_student = True
12 
13# NoneType
14result = None
15 
16# Check types
17print(type(count))       # <class 'int'>
18print(type(temperature)) # <class 'float'>
19print(type(greeting))    # <class 'str'>

Output

<class 'int'>
<class 'float'>
<class 'str'>

Variable Naming Rules

naming.py

1# Valid names
2user_name = "Alice"
3_private = 42
4totalCount2 = 100
5 
6# Invalid names (will cause errors)
7# 2nd_place = "Bob"   # Can't start with digit
8# my-var = 10         # Hyphens not allowed
9# class = "Math"      # Reserved keyword

Type Conversion

type_conversion.py

1# String to Integer
2age_str = "25"
3age_num = int(age_str)
4print(age_num + 5)  # 30
5 
6# Integer to String
7count = 42
8message = "Items: " + str(count)
9print(message)  # Items: 42
10 
11# Float to Integer (truncates)
12pi = 3.99
13print(int(pi))  # 3

Output

30
Items: 42
3

What Are Variables?

Core Data Types

Variable Naming Rules

Type Conversion

Key Takeaways

Variables & Data Types

What Are Variables?

Core Data Types

Variable Naming Rules

Type Conversion

Key Takeaways