← Errors
RuntimeError is a catch-all exception for errors that don't fit a more specific category. The most common instance is 'dictionary changed size during iteration', but it also covers thread-related errors and generator issues.
Why it happens
- •Adding or removing keys from a dictionary while iterating over it.
- •Calling a coroutine or generator in an invalid state.
- •Recursive call detected in a context that prohibits recursion.
- •Using a thread primitive incorrectly, such as releasing an unlocked lock.
Examples
Python
Code that triggers the error
d = {"a": 1, "b": 2}
for key in d:
if key == "a":
d["c"] = 3Error output
RuntimeError: dictionary changed size during iteration
How to fix it
To safely modify a dict during iteration, iterate over a copy (list(d.keys())) or collect changes and apply them after the loop. For other RuntimeErrors, read the message carefully as it describes the specific invalid operation.
Fixed code
d = {"a": 1, "b": 2}
to_add = {}
for key in d:
if key == "a":
to_add["c"] = 3
d.update(to_add)Related errors
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