[HotFix] Fix python import

[echuraev]

Tuning doesn't work after #12969.
It reports the following error:

ImportError: cannot import name 'get_const_float' from partially initialized module 'tvm.topi.utils' (most likely due to a circular import)

In this commit, I moved import relay to a function which used in a test. And it helps to fix this circular import.

To reproduce this issue, you can run the following tutorial and will see this error.

cc: @guberti, @areusch, @ekalda

[tvm-bot]

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• cc @driazati _{See #10317 for details}
• Built docs for commit 82a4393 can be found here.

_{Generated by tvm-bot}

[guberti]

If tuning doesn't work, that's a pretty big oversight on my part and a hotfix like this makes sense.

I can't seem to reproduce the issue though - here's a log of what I get when I run on the latest TVM revision.

We also have a unit test that (I believe) compiles and re-deploys the docs, with output, whenever changes are made. Here's a link to the tutorial in question - the output there looks fine.

Any ideas why I can't seem to reproduce this?

[echuraev]

Hmmm. Looks interesting. I was able to reproduce this issue on the commit: 3f0d3f2
I run on Ubuntu 20.04 with python 3.8.8. Here is my output for this script from the tutorial. And you can see that tuning doesn't work. @guberti which environment do you use?

[echuraev]

I see that someone else has the same issue: https://discuss.tvm.apache.org/t/error-of-import-topi-utils-during-autotune/13728

[guberti]

I'm on almost the exact same environment - Ubuntu 20.04 and Python 3.8.10 (see log). I wonder if this is an issue with your Python PATH environment, but I don't have any way to investigate.

I suspect the error will go away once #13051 merges, but I'm very curious what the underlying problem is - we should add a test for this.

[driazati]

I suspect this also might be related to how tvm doesn't initialize/import all nested modules, so you can end up with situations like:

>>> import tvm
>>> tvm.relay.Var
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'tvm' has no attribute 'relay'
>>> from tvm import relay
>>> tvm.relay.Var
<class 'tvm.relay.expr.Var'>

We do run the tutorials as part of the post-merge ci jobs for main, the latest successful one is here which looks like it was able to run the tutorial, though it does it in a Docker environment (you might be able to re-create that locally with python tests/scripts/ci.py docs --tutorial-pattern 'autotvm_relay_x86.py')

[junrushao]

LGTM

[guberti]

The changes themselves seem reasonable, but I'm hesitant to merge a hotfix for an issue we can't reproduce. Any chance this issue can be reproduced on Google Colab or something similar?

[masahi]

It's not just tuning, I got this error yesterday when running https://github.com/apache/tvm/blob/main/tests/python/unittest/test_meta_schedule_schedule_rule_mlt.py by python. The error doesn't happen if the script is invoked by pytest.