"Dictionary changed size during iteration" in 2.16.0 #2489
Description
In metaflow==2.16.0, the code here introduced in #2487 can raise a RuntimeError because sys.modules may be modified while being iterated:
Traceback (most recent call last):
File ".../site-packages/metaflow/cli.py", line 646, in main
start(auto_envvar_prefix="METAFLOW", obj=state)
...
File ".../site-packages/metaflow/cli_components/run_cmds.py", line 63, in before_run
obj.package = MetaflowPackage(
File ".../site-packages/metaflow/package/__init__.py", line 87, in __init__
self._mfcontent = MetaflowCodeContentV1(criteria=_module_selector)
File ".../site-packages/metaflow/packaging_sys/v1.py", line 46, in __init__
modules = sorted(modules, key=lambda x: x[0])
RuntimeError: dictionary changed size during iteration
In my case, this happened because of the hasattr check in the criteria callback, which ended up calling a module's __getattr__ which performed an import. To repro, just use the helloworld.py example and add import beartype at the top.
It's common to import stuff dynamically in Python, so iterating sys.modules while calling any code isn't safe. The code should probably make a copy.