Summary - Advanced exceptions

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.

Exercise 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__).

Show example 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__)

Test yourself

Which word is used to access the error object?
- as
- is
- to
- be
Show answer

as — as e binds the error object to the variable e.

Complete raise from e

raise RuntimeError("Error") ____ e

Show answer

raise RuntimeError("Error") from e

Match the advanced exception concepts

except (A, B)

Multi-type tuple
as e

Binds object to e
from e

Chaining keyword
format_exc

Returns trace as string

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