Chapter 26: Exceptions and Error Handling

Complete Python lesson for very beginners. Technical words are explained in simple language, and every outline topic includes a practical example, expected output, steps, and practice.

Python CourseVery Beginner Friendly15 TopicsExamples + Output20 Q&A

Chapter 26 · 15 topics

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Chapter Overview

This Python tutorial chapter covers Exceptions and Error Handling through 15 connected topics. Work through the examples in order, check the expected output, and complete the practice after each topic.

26.1 Syntax Errors
26.2 Runtime Errors
26.3 Exceptions
26.4 try
26.5 except
Plus 10 additional Python topics in this chapter.

26.1 Syntax Errors

Syntax Errors is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

It is one building block of exceptions and error handling and helps you write clearer, more predictable Python programs. For a very beginner, focus first on what goes in, what Python does, and what comes out; details become easier after you run a small example.

Technical words in simple language: Syntax Errors (a Python idea used while learning exceptions and error handling).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Syntax Errors”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.2 Runtime Errors

Runtime Errors is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

Technical words in simple language: Runtime Errors (a Python idea used while learning exceptions and error handling).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Runtime Errors”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.3 Exceptions

Exceptions is part of Exceptions and Error Handling. In simple language, it means an object that represents a runtime problem.

Technical words in simple language: Exceptions (an object that represents a runtime problem).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Exceptions”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.4 try

try is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

Technical words in simple language: try (a Python idea used while learning exceptions and error handling).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “try”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.5 except

except is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

Technical words in simple language: except (a Python idea used while learning exceptions and error handling).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “except”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.6 Multiple Exceptions

Multiple Exceptions is part of Exceptions and Error Handling. In simple language, it means an object that represents a runtime problem.

Technical words in simple language: Multiple Exceptions (an object that represents a runtime problem).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Multiple Exceptions”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.7 else

else is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

Technical words in simple language: else (a Python idea used while learning exceptions and error handling).

Python / Practical Example

age = 15
if age >= 18:
    print("adult")
else:
    print("minor")

Expected Output

minor

Step-by-Step Explanation

Test a condition.
The condition is false.
else runs the alternative block.

Practice: Re-type the example for “else”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.8 finally

finally is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

Technical words in simple language: finally (a Python idea used while learning exceptions and error handling).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “finally”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.9 raise

raise is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

Technical words in simple language: raise (a Python idea used while learning exceptions and error handling).

Python / Practical Example

age = -1
if age < 0:
    raise ValueError("age cannot be negative")

Expected Output

ValueError: age cannot be negative

Step-by-Step Explanation

Check for invalid data.
raise creates the chosen exception.
The error message explains the problem.

Practice: Re-type the example for “raise”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.10 Exception Objects

Exception Objects is part of Exceptions and Error Handling. In simple language, it means a value with data and behavior.

Technical words in simple language: Exception Objects (a value with data and behavior).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Exception Objects”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.11 Built-in Exceptions

Built-in Exceptions is part of Exceptions and Error Handling. In simple language, it means an object that represents a runtime problem.

Technical words in simple language: Built-in Exceptions (an object that represents a runtime problem).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Built-in Exceptions”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.12 Custom Exceptions

Custom Exceptions is part of Exceptions and Error Handling. In simple language, it means an object that represents a runtime problem.

Technical words in simple language: Custom Exceptions (an object that represents a runtime problem).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Custom Exceptions”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.13 Exception Chaining

Exception Chaining is part of Exceptions and Error Handling. In simple language, it means an object that represents a runtime problem.

Technical words in simple language: Exception Chaining (an object that represents a runtime problem).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Exception Chaining”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.14 Assertions

Assertions is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

Technical words in simple language: Assertions (a Python idea used while learning exceptions and error handling).

Python / Practical Example

total = 5
assert total >= 0
print("valid")

Expected Output

valid

Step-by-Step Explanation

assert checks a condition during development.
No exception occurs because the condition is true.
Do not use assertions as a substitute for user-input validation.

Practice: Re-type the example for “Assertions”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

26.15 Error-Handling Practices

Error-Handling Practices is part of Exceptions and Error Handling. In simple language, it means a Python idea used while learning exceptions and error handling.

Technical words in simple language: Error-Handling Practices (a Python idea used while learning exceptions and error handling).

Python / Practical Example

try:
    number = int("not-a-number")
except ValueError as error:
    print(type(error).__name__)

Expected Output

ValueError

Step-by-Step Explanation

Put risky conversion inside try.
Catch the specific ValueError you expect.
Handle the problem without hiding unrelated errors.

Practice: Re-type the example for “Error-Handling Practices”, change one safe input, predict the result before running it, and explain in one sentence why the result changed.

Common Beginner Mistakes

Copying code without predicting what each line does.
Ignoring the first useful error message or traceback location.
Mixing tabs/spaces or changing indentation accidentally.
Using data of the wrong type for an operation.
Trying to learn many advanced variations before mastering one small working example.

Chapter Practice

Choose three topics from this chapter and re-type their examples without copying and pasting.
For each example, change one input and predict the output first.
Explain five technical terms from this chapter in your own beginner-friendly words.
Create one small program that combines at least two chapter topics.
Keep notes about errors you made and what fixed them.

Mini Project / Challenge

Create a small Python exercise that combines at least three ideas from Exceptions and Error Handling. Start with a tiny working version, test it, then improve it one step at a time.

Choose three topics from this chapter.
Write or adapt a small Python example using those topics.
Predict the output before running the code.
Test at least one different input.
Write two sentences explaining what the program does and what you learned.

20 Questions & Answers

1. What is the main goal of Chapter 26?

The goal is to understand exceptions and error handling through small explanations, examples, and practice.

2. Should I memorize every command or method?

No. Understand the pattern, practice the common form, and learn how to read documentation when you need exact details.

3. Why are the examples small?

Small examples isolate one idea at a time, which makes errors easier to understand and fix.

4. What should I do when an example gives an error?

Read the last part of the traceback, check spelling and indentation, confirm the required package or file exists, and compare the input types with what the operation expects.

5. Why should I predict output before running code?

Prediction forces you to reason about the program instead of only copying it.

6. What should I remember about Syntax Errors?