Python Common Mistakes with Variable Names and Indentation

Variable naming and indentation errors are common when starting Python. Most can be fixed by reading the error and checking a few basic rules.

Understanding the Concept

Names are case-sensitive, so total_price and Total_Price are different. Names cannot start with a digit or use reserved keywords. An indented block must follow a statement that introduces it, such as if or for. Consistently use four spaces rather than mixing tabs and spaces. If Python reports NameError, inspect the exact spelling and execution order; if it reports IndentationError, inspect block structure and whitespace.

When and Why You Would Use This

Start with a correctly written example, then deliberately create one error at a time. A controlled experiment teaches more than copying an error message without context.

Practical Example

order_total = 40
if order_total > 20:
    print("Order exceeds 20")
print("Validation finished")

Understanding the Example

Both lines print for order_total equal to 40. Rename the first variable to Order_Total without changing the reference in the if statement and the program raises NameError. Remove indentation from the first print and it raises an indentation or syntax-related error.

Example Output

Order exceeds 20
Validation finished

Try It Yourself

Introduce a spelling mistake, repair it, then introduce an indentation mistake and repair that separately.

Common Beginner Mistakes

Changing name capitalization accidentally and creating two different identifiers.
Mixing tabs and spaces in the same block.
Indenting a statement without a matching surrounding block or failing to indent after a colon.

Key Takeaways

Python variable names are case-sensitive.
Indentation defines blocks and must be consistent.
Read NameError and IndentationError as clues to specific categories of mistakes.