import time
import threading
b = threading.Barrier(2)
class Foo:
pass
class MyStr(str):
def __hash__(self):
return super().__hash__()
def __eq__(self, other):
time.sleep(0.1)
return super().__eq__(other)
def thread():
b.wait()
time.sleep(0.05)
f2 = Foo()
f2.a = "a"
f2.b = "b"
f2.c = "c"
def main():
t1 = threading.Thread(target=thread)
t1.start()
b.wait()
f1 = Foo()
f1.a = "a"
f1.b = "b"
x = {}
x[MyStr("a")] = MyStr("a")
x.update(f1.__dict__)
t1.join()
if __name__ == "__main__":
main()Traceback (most recent call last):
File "/home/sgross/cpython/bad.py", line 44, in <module>
main()
~~~~^^
File "/home/sgross/cpython/bad.py", line 39, in main
x.update(f1.__dict__)
~~~~~~~~^^^^^^^^^^^^^
RuntimeError: dict mutated during update
Bug report
The
dict.update()modification check can be erroneously triggered by modifications to different dictionaries that happen to share the underlying keys objects.For example, in the following program, the creation and modification of the
f2object can lead to an incorrectRuntimeErrorraised in the main thread that operates on distinct dictionaries.Linked PRs
dict.update()mutation check #134815dict.update()mutation check (gh-134815) #135581dict.update()mutation check (gh-134815) #135582