RuntimeError
RuntimeError: no active exception to reraise
Traceback
Traceback (most recent call last):
File "main.py", line 4, in <module>
del d[key]
RuntimeError: no active exception to reraiseWhat causes this error
A generic runtime error condition occurred. This is used when no more specific exception type applies. Common triggers include using bare `raise` outside an exception handler and modifying iterables during iteration.
How to fix it
Read the error message carefully — it describes the specific issue. For dictionary/set modification during iteration, iterate over a copy. For asyncio issues, use the appropriate event loop management functions.
Code that causes this error
d = {"a": 1, "b": 2, "c": 3}
for key in d:
if d[key] < 2:
del d[key]Fixed code
d = {"a": 1, "b": 2, "c": 3}
for key in list(d.keys()):
if d[key] < 2:
del d[key]About RuntimeError
RuntimeError is a generic exception class for errors that do not fall into any specific category. It is used as a catch-all when the situation does not warrant a more specific exception type. In practice, RuntimeError is raised in several well-known scenarios: using `raise` without an active exception (in an except block), modifying a dictionary, set, or deque while iterating over it, calling `generator.throw()` or `generator.close()` improperly, and in various library-specific contexts.
The asyncio library raises RuntimeError when attempting to run an event loop that is already running, or when performing async operations without a loop. Many third-party libraries also raise RuntimeError for configuration errors, state violations, and invariant failures. When you encounter a RuntimeError, the message is usually descriptive enough to identify the specific cause, since the exception class itself is intentionally broad.
Common scenarios
Infinite recursion from missing or incorrect base cases
Modifying dictionaries or sets during iteration
Calling generators or coroutines in unsupported ways
Using asyncio event loops incorrectly or attempting to nest them