ruff/crates/red_knot_python_semantic/resources/mdtest/exception/basic.md

Exception Handling

Single Exception

import re

try:
    help()
except NameError as e:
    reveal_type(e)  # revealed: NameError
except re.error as f:
    reveal_type(f)  # revealed: error

Unknown type in except handler does not cause spurious diagnostic

from nonexistent_module import foo  # error: [unresolved-import]

try:
    help()
except foo as e:
    reveal_type(foo)  # revealed: Unknown
    reveal_type(e)  # revealed: Unknown

Multiple Exceptions in a Tuple

EXCEPTIONS = (AttributeError, TypeError)

try:
    help()
except (RuntimeError, OSError) as e:
    reveal_type(e)  # revealed: RuntimeError | OSError
except EXCEPTIONS as f:
    reveal_type(f)  # revealed: AttributeError | TypeError

Dynamic exception types

def foo(
    x: type[AttributeError],
    y: tuple[type[OSError], type[RuntimeError]],
    z: tuple[type[BaseException], ...],
):
    try:
        help()
    except x as e:
        reveal_type(e)  # revealed: AttributeError
    except y as f:
        reveal_type(f)  # revealed: OSError | RuntimeError
    except z as g:
        # TODO: should be `BaseException`
        reveal_type(g)  # revealed: @Todo(full tuple[...] support)

Invalid exception handlers

try:
    pass
# error: [invalid-exception-caught] "Cannot catch object of type `Literal[3]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
except 3 as e:
    reveal_type(e)  # revealed: Unknown

try:
    pass
# error: [invalid-exception-caught] "Cannot catch object of type `Literal["foo"]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
# error: [invalid-exception-caught] "Cannot catch object of type `Literal[b"bar"]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
except (ValueError, OSError, "foo", b"bar") as e:
    reveal_type(e)  # revealed: ValueError | OSError | Unknown

def foo(
    x: type[str],
    y: tuple[type[OSError], type[RuntimeError], int],
    z: tuple[type[str], ...],
):
    try:
        help()
    # error: [invalid-exception-caught]
    except x as e:
        reveal_type(e)  # revealed: Unknown
    # error: [invalid-exception-caught]
    except y as f:
        reveal_type(f)  # revealed: OSError | RuntimeError | Unknown
    except z as g:
        # TODO: should emit a diagnostic here:
        reveal_type(g)  # revealed: @Todo(full tuple[...] support)