Refactor backend loading #9551

anntzer · 2017-10-24T04:35:58Z

This is preliminary work towards fixing the runtime detection of default
backend problem (the first step being to make it easier to check whether
a backend can be loaded). No publically visible API is changed.

Backend loading now defines default versions of backend_version,
draw_if_interactive, and show using the same inheritance strategy as
builtin backends do.

The _Backend class had to be moved to the end of the module as
FigureManagerBase needs to be defined first. The ShowBase class had
to be moved even after that as it depends on the _Backend class.

PR Summary

PR Checklist

Has Pytest style unit tests
Code is PEP 8 compliant
New features are documented, with examples if plot related
Documentation is sphinx and numpydoc compliant
Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

dstansby · 2017-11-16T10:42:38Z

lib/matplotlib/backend_bases.py

@@ -3362,3 +3250,129 @@ def set_message(self, s):
            Message text
        """
        pass
+


Is this block just a big copy/paste? (so we don't have to bother reviewing the code if it is)

It is, except for the fact that the FigureManager attribute now defaults to FigureManagerBase.

anntzer · 2018-05-25T06:02:12Z

@jklymak If you want to help getting #9795 in, this is the first step towards it :) Just rebased it (on top of #11305, to avoid immediately yet another rebase).

jklymak · 2018-05-25T16:20:23Z

lib/matplotlib/backends/__init__.py

+    backend_name = (name[9:] if name.startswith("module://")
+                    else "matplotlib.backends.backend_{}".format(name.lower()))
+    backend_mod = importlib.import_module(backend_name)
+    Backend = type("Backend", (_Backend,), vars(backend_mod))


Can you add a comment explaining this bit of magic? I get that it returns a base _Backend class, but am not quite sure what vars(backend_mod) does.

vars(obj) returns the attributes of obj as a dict. In the case of a module, that's basically the module's contents.

So effectively it's as if I'm running all of the module's code (of course, not a second time) from within a class Backend(_Backend): ... context, and refetching attributes from that class. The point being that the base _Backend class can provide default implementations of backend_version, show, draw_if_interactive through inheritance rather than pylab_setup having to do it manually. Will add a comment to that effect, but does that sound good?

yeah, not objecting to the magic at all, but I think a short comment to help those of us with lesser python skills know whats going on would help make sure the code stays maintained...

added comment.

tacaswell · 2018-05-26T00:22:28Z

lib/matplotlib/backends/__init__.py

+    # Create a local Backend class whose body corresponds to the contents of
+    # the backend module.  This allows the Backend class to fill in the missing
+    # methods through inheritance.
+    Backend = type("Backend", (_Backend,), vars(backend_mod))


So we create the class, use the inheritance to fill in the missing functions and then return class level functions (which 'forget' they were part of the class)?

That is quite clever.

To check, if a backend is already using @_Backend.export then there should be nothing extra we need to provide?

Indeed, backends that were using @_Backend.export don't really need that anymore (the contents of the local _Backend class could just be dumped at the module level (or alternatively they could just do without the temporary creation of a new Backend class))... except for one thing: the _Backend class still allows inheritance between backends, so that e.g. _BackendQt5Agg can inherit from _BackendQt5.

tacaswell · 2018-05-26T00:24:06Z

lib/matplotlib/backends/backend_ps.py

@@ -1699,8 +1699,7 @@ def pstoeps(tmpfile, bbox=None, rotated=False):
    shutil.move(epsfile, tmpfile)


-class FigureManagerPS(FigureManagerBase):
-    pass
+FigureManagerPS = FigureManagerBase


There is a very subtle API change in here if people are looking at __name__, __module__, or __file__ of these classes. I am not sure if that is worth an API change note or not.

I added an API note. The real intent here is the following:

I think the "correct" way to refer to a backend's FigureCanvas, FigureManager, etc. class is under the unsuffixed names (FigureCanvas instead of FigureCanvasPS, etc.) The reason is that 1) these unsuffixed names need to be defined anyways for the backend machinery to pick them up, and 2) some of these classes (FigureManager, Toolbar, though not FigureCanvas of course) can be shared between multiple backends (for example, the xxxcairo backends and mplcairo just reuses the FigureManager classes for each of the GUI toolkits).

So sure, I can define (e.g.) FigureManagerQt5 and FigureManagerQt5Agg and FigureManagerQt5Cairo and FigureManagerMplCairoQt to all be aliases (or trivial subclasses) of one another, but that's just muddying the picture IMO; promoting the use of the same FigureManager name everywhere seems clearer.

tacaswell · 2018-05-28T21:21:07Z

This needs a rebase.

@anntzer Please self-merge once CI passes.

anntzer · 2018-05-29T00:30:56Z

Self-merging per #9551 (comment).

anntzer force-pushed the backend-loading branch 2 times, most recently from 81d7c52 to c1dfd56 Compare October 24, 2017 07:46

anntzer closed this Oct 24, 2017

anntzer self-assigned this Oct 24, 2017

anntzer reopened this Oct 25, 2017

anntzer force-pushed the backend-loading branch from c1dfd56 to 54e3169 Compare October 25, 2017 05:26

anntzer removed their assignment Oct 25, 2017

anntzer force-pushed the backend-loading branch from 54e3169 to 439338d Compare October 25, 2017 05:27

anntzer force-pushed the backend-loading branch from 439338d to e45d8b0 Compare November 13, 2017 00:31

anntzer mentioned this pull request Nov 16, 2017

Backend switching #9795

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dstansby reviewed Nov 16, 2017

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anntzer force-pushed the backend-loading branch 2 times, most recently from 33fb09d to 56858ae Compare November 17, 2017 21:36

anntzer force-pushed the backend-loading branch from 56858ae to c6e21f4 Compare December 7, 2017 05:54

anntzer force-pushed the backend-loading branch from c6e21f4 to a16e3ec Compare December 22, 2017 07:13

anntzer force-pushed the backend-loading branch from a16e3ec to 2c73aba Compare December 29, 2017 23:59

anntzer force-pushed the backend-loading branch from 2c73aba to 181cb70 Compare January 9, 2018 06:50

anntzer added the status: needs rebase label Apr 5, 2018

anntzer force-pushed the backend-loading branch from 181cb70 to 3b2d407 Compare May 25, 2018 05:58

anntzer removed the status: needs rebase label May 25, 2018

anntzer force-pushed the backend-loading branch from 3b2d407 to af90b80 Compare May 25, 2018 06:01

jklymak reviewed May 25, 2018

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anntzer force-pushed the backend-loading branch from af90b80 to 3a795a3 Compare May 25, 2018 21:03

jklymak approved these changes May 25, 2018

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tacaswell added this to the v3.0 milestone May 26, 2018

tacaswell reviewed May 26, 2018

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anntzer force-pushed the backend-loading branch 2 times, most recently from 7b8b41b to 36fab4c Compare May 26, 2018 00:41

tacaswell approved these changes May 28, 2018

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Revival of the backend loading refactor.

617c5d6

anntzer force-pushed the backend-loading branch from 36fab4c to 617c5d6 Compare May 28, 2018 22:45

anntzer merged commit ad44a7e into matplotlib:master May 29, 2018

anntzer deleted the backend-loading branch May 29, 2018 00:31

Readon mentioned this pull request Jun 12, 2018

matplotlib's dependency on qt should be optional msys2/MINGW-packages#3218

Closed

anntzer mentioned this pull request Sep 7, 2019

Various backend cleanups. #15211

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Refactor backend loading #9551

Refactor backend loading #9551

anntzer commented Oct 24, 2017 •

edited

dstansby Nov 16, 2017

anntzer Nov 16, 2017

anntzer commented May 25, 2018

jklymak May 25, 2018

anntzer May 25, 2018

jklymak May 25, 2018

anntzer May 25, 2018

tacaswell May 26, 2018

anntzer May 26, 2018

tacaswell May 26, 2018

anntzer May 26, 2018 •

edited

tacaswell commented May 28, 2018

anntzer commented May 29, 2018

Refactor backend loading #9551

Refactor backend loading #9551

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anntzer commented Oct 24, 2017 • edited

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anntzer commented May 25, 2018

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anntzer May 26, 2018 • edited

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tacaswell commented May 28, 2018

anntzer commented May 29, 2018

anntzer commented Oct 24, 2017 •

edited

anntzer May 26, 2018 •

edited