[yt-users] yt unable to find sip module

[Matthew Turk]

Hi Gary,

Sorry about the troubles!  Nathan's definitely provided some good
suggestions; let's see if we can figure out what's up.  I have some
questions and ideas.

On Mon, Sep 2, 2013 at 5:32 PM, Gary Foreman <gforema2 at illinois.edu> wrote:
> Hello,
>
> Suddenly my yt distribution seems to be broken because it cannot find the
> module sip. Sip appears to be a python/C interface that is called by
> matplotlib.pyplot. I have tried a few things to resolve the issue, none of
> which have worked. I've tried: yt update --all, pip install sip, and apt-get
> install yt using the repository mentioned on the Get YT page. pip install
> and apt-get install fail for separate reasons, which I can explain in a
> future email if necessary.
>
> Since first encountering this problem, I have updated my OS because I
> realized I was using an outdated version of Ubuntu. I am now running Ubuntu
> 12.4 LTS. The OS update did not resolve the issue.

I think the best bet, right now, is *just* the install_script.sh
method for Ubuntu.

>
> It seems worth mentioning that the default system python distribution is
> working fine and I am able to import pyplot as well as sip without a
> problem. During a quick search of the yt distribution, I did not find the
> same sip related files that I have in my system's python distribution.
>
> Also, as of Friday, things are working fine with the yt distribution I have
> on my Mac laptop.

That's good to hear!  :)

>
> Thanks very much in advance for your help. Please let me know if you would
> like me to post some of the error messages I have received from the few
> solutions that I've tried.

Here's what I suspect is going on.  A recent change to Matplotlib
modifies the type of backend that is selected by default for pyplot.
We've seen issues crop up on OSX recently from this change as well,
where the python installed is not built in such a way as to enable the
given frontend.  On Linux, this would manifest as not being able to
access Qt -- the backend in particular is PyQt4, and it depends on
SIP, which as you and Nathan noted is a mechanism for interfacing C++
and Python code.

Unfortunately, the problems run a bit deeper, in that yt's base
install builds a Python that is distinct from the system's python, and
so binary modules may not work across those two.  This further causes
problems because the Qt python wrappings will have to be built against
*yt's* python, and then that just builds an enormous stack of
dependencies that's tough to resolve.  Typically what we do is simply
not enable the PyQt4 backend.  One issue with the backend selection
process is that it is often fatal; rather than defaulting to a backend
that works, the matplotlib/pyplot interface just fails out.

What I would suggest as a broad strategy is: do not attempt to get the
yt python and system python to work together, and don't try to get the
PyQt4 bindings that are apt-get-able to work with the yt-installed
Python -- it's just going to dig deeper and deeper.  Instead, turn off
the PyQt4 backend and use Agg, similar to how Nathan suggested, but
switching "TkAgg" for "Agg".

But, this also means no interactive pyplot sessions.  This is an
enormous problem, and unfortunately getting everything to play nicely
is somewhat difficult for us as a (relatively) small project to
manage.  What we are attempting to do is instead step aside the
packaging issue and *stop* attempting to create a full yt stack.  Our
first discussion of this was on yt-dev the other day:

http://lists.spacepope.org/pipermail/yt-dev-spacepope.org/2013-August/003386.html

So, short term: switch the backend to Agg, which should fix things
from that perspective but won't give interactive plotting widgets.
Longer term, we are going to clean up the yt house to play much, much
nicer with both distributions (like Ubuntu) and with python
distributions (like Conda/Anaconda) to keep this from happening in the
future and to make way more functionality available.

Let me know if that fix works!

-Matt

>
> Gary
>
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