Errors, Debugging & Exception Basics

1. What Is an Error?

An error occurs when Python cannot execute your code as intended. Errors are normal when learning programming. The important skill is learning how to read the error and locate the problem.

print("Hello"

The closing parenthesis is missing, so Python cannot correctly understand the statement.

2. Syntax Errors

A syntax error occurs when Python code does not follow the language's syntax rules.

if 10 > 5
    print("Yes")

The colon after the condition is missing.

3. Runtime Errors

A runtime error happens while the program is running. The syntax may be valid, but an operation cannot be completed.

number = 10
print(number / 0)

Python cannot divide a number by zero, so this produces aZeroDivisionError.

4. NameError

A NameError can occur when Python tries to use a variable or name that has not been defined.

sales = 50000
print(total_sales)

total_sales was never defined.

5. TypeError

A TypeError can occur when an operation is performed on incompatible types.

age = 20
print(age + " years")

Here Python is asked to add an integer and a string.

6. IndexError

IndexError can occur when you try to access a list position that does not exist.

sales = [100, 200, 300]

print(sales[5])

7. Logical Errors

A logical error is different. The program runs, but it produces the wrong result because the logic is incorrect.

price = 100
quantity = 5

total = price + quantity

print(total)

The code runs, but the calculation should use multiplication, not addition.

8. A Simple Debugging Process

1. Read the error message.
2. Look at the line number.
3. Understand what Python expected.
4. Check variable names and values.
5. Test a smaller part of the program.
6. Fix the problem and run the code again.

9. Handling Errors with try and except

Sometimes we expect that an operation might fail. Python allows us to handle certain runtime errors with try andexcept.

try:
    number = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero")

Python attempts the code inside try. If the specified exception occurs, the except block runs.

10. Handling Different Exceptions

try:
    value = int("abc")
except ValueError:
    print("Invalid number")

int("abc") cannot convert the text to an integer, so Python raises a ValueError.

11. Debugging Data Analytics Code

Debugging becomes especially important when processing business data. A small error in a calculation can produce incorrect analytical results.

def revenue(price, quantity):
    return price * quantity

sales = revenue(5000, 4)

print(sales)

Before trusting the result, check the inputs, calculation, and expected output.