tree b42dd84a1027d5854683f7ddbd27dfed33cff771
parent 6d336c5635c3ae0bf0d70309227f8e9e127bb9d8
author Jason Lowe-Power <jason@lowepower.com> 1634148396 -0700
committer Jason Lowe-Power <power.jg@gmail.com> 1634760731 +0000

python: Add check to SimObject for __init__

When extending a SimObject by subclassing, if you don't call
`super().__init__()` you get a confusing infinite recursion error. The
infinite recursion occurs because SimObject overrides `__getattr__`. So,
if an attribute is accessed that is set in SimObject.__init__ but that
function hasn't been called there's a problem.

This patch adds another member variable to track if __init__ has been
called. This member variable is set to False in the *meta class*  so
that it will always be available, even if __init__ has not been called.
There is one check for whether init has been called in the __getattr__
function. This is where I have experienced prior issues. This function
could be called from other SimObject functions, if needed.

With this change, a helpful error is shown telling the user to be sure
to call super().__init__ in the specific class that is missing the call.

Note: I have been bitten by this an embarrassing number of times. A
helpful error message would have saved me many hours.

Change-Id: Id919c540b23fc2783e203ef625bce3000ba808a9
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/51568
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>