Variables and Data Types

In computer programming, a Variable is a reserved memory location to store values. This means that when you create a variable, you reserve some space in memory (RAM). Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory.

1. Dynamic Typing in Python

Python is a Dynamically Typed language. Unlike languages such as C++ or Java, you do not need to declare the type of a variable when you create one. The type is determined during runtime based on the value assigned to the variable.

# The interpreter assigns the 'integer' type to 'age'
age = 25

# The same variable can later hold a different type
age = "Twenty Five" 

2. Fundamental Data Types

Python provides several built-in data types that are used to define the operations possible on them and the storage method for each of them.

I. Numeric Types

• Integers (int): Whole numbers, positive or negative, without decimals, of unlimited length.
• Floating Point Numbers (float): Numbers with one or more decimals. Python also supports scientific notation with e to indicate the power of 10.
• Complex Numbers (complex): Written with a "j" as the imaginary part (e.g., 3+5j).

II. Sequence Types

• Strings (str): Contiguous sets of characters represented in quotation marks. Python does NOT have a character type; a single character is simply a string of length 1.
• Lists & Tuples: Ordered collections of items (covered in depth in future modules).

III. Boolean Type (bool)

• Represents one of two values: True or False. Used extensively in conditional logic and flow control.

3. Variable Naming Conventions (PEP 8)

To maintain a professional codebase, you should follow the PEP 8 style guide for Python code.

1. Snake Case: Separate words with underscores (e.g., user_profile_id).
2. Case Sensitivity: Value and value are distinct variables.
3. No Keywords: You cannot use reserved keywords (like if, else, while, def) as variable names.
4. Meaningful Identifiers: Avoid abstract names like temp or x. Use names that describe the data's purpose.

4. Deep Dive: Everything is an Object

In Python, everything is an object. When you assign x = 10, Python creates an integer object with the value 10 and makes the variable x a reference (pointer) to that object.

The id() and type() functions:

• id(variable): Returns the unique memory address of the object.
• type(variable): Returns the data type of the object.

x = 10
print(id(x))   # Prints the memory location
print(type(x)) # Prints <class 'int'>

Interview Pro-Tips: Mutable vs. Immutable

Interviewers frequently ask about the difference between Mutable and Immutable types.

• Immutable: Types that cannot be changed after they are created (int, float, str, tuple). If you modify an immutable variable, Python creates a new object and updates the variable's reference.
• Mutable: Types that can be changed in place (list, dict, set). Modifying them does not change their memory address.