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__import__ too eager, make it lazy #161721
Description
Bug report
We have an inconsistency:
import <module> -> ModuleType | LazyImportType
lazy import <module> -> ModuleType | LazyImportType
__lazy_import__(<module>) -> ModuleType | LazyImportType
importlib.import_module(<module>) -> ModuleType
importlib.__import__(<module>) ->ModuleType
__import__(<module>) -> ModuleType
At its core, the issue seems to be that __lazy_import__ checks lazy filters, but __import__ doesn't.
Consider:
import sys
def my_filter(importing, imported, fromlist):
return True
sys.set_lazy_imports_filter(my_filter)
sys.set_lazy_imports('all')
import json
print(type(globals()['json']))Outputs <class 'lazy_import'> as expected.
But switching the import json to json = __import__('json') (or importlib.import_module or importlib.__import__) outputs <class 'module'>.
Not only is that inconsistent with import stmt, it's inconsistent with lazy import. Consider:
import sys
def my_filter(importing, imported, fromlist):
return False
sys.set_lazy_imports_filter(my_filter)
lazy import json
print(type(globals()['json']))The output changes depending on True / False in the filter, which is intended. It also works if I switch out lazy import json for json = __lazy_import__('json').
CPython versions tested on:
3.15
Operating systems tested on:
Windows
Activity
picnixz commentedon Nov 10, 2026
Unless this was documented differently I believe this is the correct behavior though.
__import__is a low-level primitive you are not meant to call directly and it would make more sense to me that it remains as is.cc @DinoV @pablogsal
picnixz commentedon Nov 11, 2026
Rationale why I believe so: in some cases, you might want to have a primitive that ignores any existing filters and bypasses the "all" lazy mode in case you need an eager import, and i believe
__import__should do that. As for__lazy_import__, I believe it should return either a real or true module module since it doesn't know whether it was already imported I guess (and we also removed the "no lazy import" mode I think).OTOH, if it's easier to bring the code to parity, we can consider it. But that could break existing projects that relied on the fact that
__import__is unconditinally eager. I haven't read the PEP in its entirety but I'd like to know first if the original specs considered this or not.JadenV15 commentedon Nov 12, 2026
@picnixz
__import__bypasses lazy filters; how can I respect lazy filters? There's no__dynamically_import_while_respecting_lazy__().__import__bypasses lazy filters but__lazy_import__doesn't. How can this inconsistency be explained? What if I want__lazy_import__to bypass lazy filters too?[-]__import__ too greedy, make it lazy[/-][+]__import__ too eager, make it lazy[/+]picnixz commentedon Nov 12, 2026
As I said, if the PEP does not specify the behavior of
__import__it might be tricky to change it. This is why I asked whether there was something about it and why I asked the PEP authors first.JadenV15 commentedon Nov 12, 2026
Edited to include examples from
importlibpicnixz commentedon Nov 12, 2026
I looked at the PEP and https://peps.python.org/pep-0810/#unchanged-semantics says:
So this is working as intended.
[-]__import__ too eager, make it lazy[/-][+]`__import__` too eager, make it lazy[/+]