RuntimeError: dictionary changed size during iteration

[satorulab]

[2022-04-26 03:46:13,996] ERROR in app: Exception on /status [GET]
Traceback (most recent call last):
File "/root/.local/share/virtualenvs/app-4PlAip0Q/lib/python3.7/site-packages/flask/app.py", line 2447, in wsgi_app
response = self.full_dispatch_request()
File "/root/.local/share/virtualenvs/app-4PlAip0Q/lib/python3.7/site-packages/flask/app.py", line 1952, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/root/.local/share/virtualenvs/app-4PlAip0Q/lib/python3.7/site-packages/flask/app.py", line 1821, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/root/.local/share/virtualenvs/app-4PlAip0Q/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
raise value
File "/root/.local/share/virtualenvs/app-4PlAip0Q/lib/python3.7/site-packages/flask/app.py", line 1950, in full_dispatch_request
rv = self.dispatch_request()
File "/root/.local/share/virtualenvs/app-4PlAip0Q/lib/python3.7/site-packages/flask/app.py", line 1936, in dispatch_request
return self.view_functionsrule.endpoint
File "src/server.py", line 143, in status
'store': store.status(),
File "/app/src/store.py", line 33, in status
for key in self.dfs:
RuntimeError: dictionary changed size during iteration