[issue18831] importlib.import_module() bypasses builtins.__import__

[Brett Cannon]

Brett Cannon  added the comment:

I'm calling it and saying people are not expecting these semantics.

--
resolution:  -> not a bug
stage: test needed -> resolved
status: open -> closed

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[issue18831] importlib.import_module() bypasses builtins.__import__

[Terry J. Reedy]

Terry J. Reedy added the comment:

Looking at the actual doc:
"importlib.__import__(name, globals=None, locals=None, fromlist=(), level=0) An 
implementation of the built-in __import__() function."

I think this is pretty clear that builtin.__import__ has no effect unless 
directly called.

"importlib.import_module(name, package=None)...The import_module() function 
acts as a simplifying wrapper around importlib.__import__()."

The word 'wrapper' implies that import_module calls __import__, but you say it 
currently does not. So if you want to keep the code as is, I would change 'acts 
as a simplifying wrapper around' to 'is a simplified version of', which makes 
no promises.

Do you really want people to directly call importlib.__import__? If not, maybe 
the nearly empty entry should be deleted and the entry for import_module 
changed to make no reference to it.

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[issue18831] importlib.import_module() bypasses builtins.__import__

[Brett Cannon]

Brett Cannon added the comment:

help(__import__) doesn't mention anything about overriding the function. I 
already touched up the stdlib docs for builtins.__import__ to strongly advise 
you don't override the function.

As for overriding importlib.__import__, it won't do anything; the code for 
importlib.import_module() cuts through the cruft in __import__ that is unneeded 
and skips straight to the relevant code.

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[issue18831] importlib.import_module() bypasses builtins.__import__

[Terry J. Reedy]

Terry J. Reedy added the comment:

Adding something like '(not builtins.__import__)' or '(different from 
builtins.__import__') after 'importlib.__import__' should reduce the 
possibility of confusing the two and expecting something that will not happen.

You might check the doc for (builtins.)__import__ to make sure it does not 
promise anything that is no longer true.

What happens if people monkeypatch importlib.__import__?

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[issue18831] importlib.import_module() bypasses builtins.__import__

[Brett Cannon]

Brett Cannon added the comment:

builtins.__import__ and importlib.__import__ are different objects.

This isn't about whether this is whole situation is a bug per-se, but whether 
users expect that overriding builtins.__import__ will affect all import-related 
code in the stdlib and if that's reasonable.

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[issue18831] importlib.import_module() bypasses builtins.__import__

[Terry J. Reedy]

Terry J. Reedy added the comment:

Perhaps I am confused because I did not notice the switch between 
builtins.__import__ and importlib.__import__ -- and I do not know the relation 
between the two, if indeed they are two and not one. What I read and understood 
is
* importlib.import_module doc say it calls ???.__import__;
* importlib.import_module code does not call ???.__import__;
it instead calls _gcd_import (for good reasons).

If the claim and reality disagree, because ??? is effectively the same in both 
statements, then either code or doc could be changed.

If importlib.__import__ and builtins.__import__ are different objects, and the 
doc is clear about that, then no one should expect that 'calls 
importlib.__import__' means 'calls builtins.__import__'.

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[issue18831] importlib.import_module() bypasses builtins.__import__

[Brett Cannon]

Brett Cannon added the comment:

Not sure what doc discrepancy you are talking about, Terry. The docs for 
importlib are totally accurate which means no one has been accidentally mislead 
by them. This bug is about whether importlib.import_module() bypassing 
builtins.__import__ is a big enough deal to change or not.

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[issue18831] importlib.import_module() bypasses builtins.__import__

[Terry J. Reedy]

Terry J. Reedy added the comment:

The discrepancy between doc and code should be eliminated. In this case, it 
seems the doc should be changed (in 3.3 as well). Would 'not' in the right 
place suffice?

--
nosy: +terry.reedy

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[issue18831] importlib.import_module() bypasses builtins.__import__

[Brett Cannon]

New submission from Brett Cannon:

Not sure if anyone really cares about this (I don't, but I figured I should at 
least let it be known), but I realized that importlib.import_module() bypasses 
builtins.__import__ by calling directly into the innards of importlib 
(specifically _gcd_import() which skips all the extra setup that __import__ 
entails and which is unnecessary for programmatic imports).

The docs for importlib.import_module() clearly state it uses 
importlib.__import__, but I'm not sure if anyone would be surprised if they 
replaced builtins.__import__ and found that importlib.import_module() was doing 
an end-run around their custom import system, especially since we are promoting 
importlib.import_module() over calling builtins.__import__ directly.

--
components: Library (Lib)
messages: 196144
nosy: brett.cannon
priority: normal
severity: normal
stage: test needed
status: open
title: importlib.import_module() bypasses builtins.__import__
type: behavior
versions: Python 3.4

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