Summary - Advanced exceptions
- Python course
- Intermediate
- Lesson 87/116
- 5 min
Combine multiple except, chaining and traceback to write an error reporter.
Summary - Advanced exceptions
In this group you learned advanced exception-handling techniques. Multiple except blocks catch different types; the except (A, B): tuple form matches several types in one block. With as e you bind the error object to a variable.
raise X from e builds a chain; the __cause__ attribute gives access to the original error. traceback.format_exc() returns the full stack trace as a string. These tools make error handling robust in production applications.
Mini task: catch and chain
In the summary task you'll catch an error and convert it to another. The inner try raises ValueError; the except ValueError as e: block does raise RuntimeError("conversion") from e. The outer except RuntimeError as e: prints the type and cause.
This task shows chaining, as e and type-info extraction together. The output is two lines: first the new error type, then the cause type.
Practice Chain and print types
Write nested try. In the inner block do value = int("abc"); in except ValueError as e: write raise RuntimeError("conversion") from e. In the outer except RuntimeError as e: write print(type(e).__name__) and print(type(e.__cause__).__name__).
Starter code
# Write nested try
# Inner: convert ValueError to RuntimeError
# Outer: print type and cause typeSample solution
# Write nested try
try:
# Inner: convert ValueError to RuntimeError
try:
value = int("abc")
except ValueError as e:
raise RuntimeError("conversion") from e
# Outer: print type and cause type
except RuntimeError as e:
print(type(e).__name__)
print(type(e.__cause__).__name__)Expected output
RuntimeError ValueError
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which word is used to access the error object?
- as Correct answer
- is
- to
- be
Explanation: as e binds the error object to the variable e.
2 Complete raise from e
raise RuntimeError("Error") ____ eraise RuntimeError("Error") from eExplanation: The from e clause chains the original error.
3 Match the advanced exception concepts
| Term | Meaning |
|---|---|
except (A, B) |
Multi-type tuple |
as e |
Binds object to e |
from e |
Chaining keyword |
format_exc |
Returns trace as string |