I've also been thinking about this lately. I can remember being confused the first time I saw "ImportError: cannot import name X". As there are multiple things that can cause this error, it took me a while to find a stackoverflow post that suggested that this might be due to circular imports. After learning this, I still had to read a few sources to understand what circular imports were and how to fix the problem.

A quick stackoverflow search reveals that people frequently have questions about this error message: https://www.google.com/search?q=stackoverflow+python+import+error&oq=stackoverflow+python+import+error&aqs=chrome..69i57j0j69i64.6423j0j7&sourceid=chrome&ie=UTF-8#q=site:stackoverflow.com+python+importerror+%22cannot+import+name%22

At the very least, it would be nice if the error message could differentiate between different causes for this error. Ideally, however, I'd love if for circular imports, it included text on what they are and how to resolve them.

On Tue, Jun 13, 2017 at 6:10 PM, Mahmoud Hashemi <mahmoud@hatnote.com> wrote:

I didn't interpret the initial email as wanting an error on *all* circular imports. Merely those which are unresolvable. I've definitely helped people diagnose circular imports and wished there was an error that called that out programmatically, even if it's just a string admonition to check for circular imports, appended to the ImportError message.

On Tue, Jun 13, 2017 at 1:43 PM, Chris Angelico <rosuav@gmail.com> wrote:
On Wed, Jun 14, 2017 at 6:35 AM, Barry <barry@barrys-emacs.org> wrote:
> On 13 Jun 2017, at 20:13, Antoine Rozo <antoine.rozo@gmail.com> wrote:
>
> But circular imports are sometimes needed in modules.
> For example when you have two classes in two different modules that
> reference each other in their methods (and because you can't pre-declare
> classes like in C++).
>
>
> Really? It has always been a strong sign of a design bug in all the cases I
> have ever seen.
> The example you suggest always fails when I accidentally write it.
>
> Pylint will certainly shout loud that this case is an error.
>

Depends on your definition of "circular". Consider this:

# __init__.py
from flask import Flask
app = Flask(__name__)
from . import views

# views.py
from . import app
@app.route("/")
def home():
...

Technically this is circular. During the loading of __init__, views
will be imported, which then imports something from __init__. But it's
perfectly well-defined (there's no way that views will ever be the
first one imported, per the rules of packages) and it makes good
sense. An error on circular imports, or even a warning, would be very
annoying here.

ChrisA

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