ENH: allow matplotlib.use after getbackend #12608

jklymak · 2018-10-24T02:23:59Z

PR Summary

Closes the long-desired ability to just call matplotlib.use so long as another GUI backend hasn't been started:

Closes #12362 (for example)

import matplotlib
import matplotlib.pyplot as plt

matplotlib.use('Qt5Agg')
print('backend:', matplotlib.get_backend())
if not matplotlib.get_backend() == 'MacOSX':
    matplotlib.use('MacOSX')
print('backend:', matplotlib.get_backend())

plt.plot(range(10))
plt.show()
matplotlib.use('Qt5Agg')

With this PR:

$ pythonw testgetbackend.py
backend: Qt5Agg
backend: MacOSX
Traceback (most recent call last):
  File "testgetbackend.py", line 11, in <module>
    matplotlib.use('Qt5Agg')
  File "/Users/jklymak/matplotlib/lib/matplotlib/__init__.py", line 1355, in use
    switch_backend(name)
  File "/Users/jklymak/matplotlib/lib/matplotlib/pyplot.py", line 222, in switch_backend
    newbackend, required_framework, current_framework))
ImportError: Cannot load backend 'Qt5Agg' which requires the 'qt5' interactive framework, as 'macosx' is currently running

Before:

$ pythonw testgetbackend.py
testgetbackend.py:3: UserWarning: matplotlib.pyplot as already been imported, this call will have no effect.
  matplotlib.use('Qt5Agg')
backend: MacOSX
backend: MacOSX
testgetbackend.py:11: UserWarning: matplotlib.pyplot as already been imported, this call will have no effect.
  matplotlib.use('Qt5Agg')

PR Checklist

Has Pytest style unit tests
Code is Flake 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

anntzer · 2018-10-24T07:57:24Z

lib/matplotlib/__init__.py


    force : bool, optional
        If True, attempt to switch the backend.  This defaults to
-        False.
+        True.


Mention that this will raise ImportError on failure, which occurs if an incompatible event loop has already started.

anntzer

except for minor doc improvement

anntzer · 2018-10-24T07:58:47Z

lib/matplotlib/__init__.py

@@ -1292,7 +1292,7 @@ def __exit__(self, exc_type, exc_value, exc_tb):
        self.__fallback()


-def use(arg, warn=True, force=False):
+def use(arg, warn=False, force=True):


I guess it's very remotely an API break in the sense that some previously invalid calls to use() would raise a warning and do nothing whereas they will now throw an exception, but I'm not sure if it's worth an API note :)

API note added. As per below I wonder if we really want to stick closer to the original behaviour and trap the Error, warn, and not switch the backend.

tacaswell · 2018-10-24T12:56:27Z

This is the API change we decided not to make for 3.0.

I am still skeptical, but slowing coming around to this being the right path.

jklymak · 2018-10-24T14:39:52Z

I thought the API discussion was about the role of rcParams in all this. But since that’s what we do now, changing that can wait.

Of course the way things are before this PR we could have been telling people to use Force=True

jklymak · 2018-10-24T15:45:51Z

BTW, I'd also be fine w/

import matplotlib
import matplotlib.pyplot as plt

matplotlib.use('Qt5Agg')
plt.plot(range(10)); plt.show()
matplotlib.use('MacOSX')

warning and doing nothing, rather than throwing an ImportError. It'd be easy to trap the ImportError.

anntzer · 2018-10-24T17:36:12Z

It's not as if it was particularly hard for the end user to catch the import error, and not everyone reads warnings (in the long term I'd like to get rid of force and warn, which are kind of silly now that backend switching works, but that's for another day...).

jklymak · 2018-10-24T18:27:34Z

@anntzer, I agree, but that behaviour is not as key to me as the ability for matplotlib.use to actually change the backend before the GUI has started.

tacaswell · 2018-10-25T02:02:27Z

re-milestoned out of 3.0.1 as I want to think about this a bit more not under the pressure of "we need to get out a bug-fix-release that works on py3.7.1"

jklymak · 2018-10-25T23:12:45Z

Just to get folks thinking about this, what are the cons of this change?

…608-on-v3.0.x Backport PR #12608 on branch v3.0.x (ENH: allow matplotlib.use after getbackend)

tacaswell · 2018-10-31T20:08:40Z

On a bit more consideration, I suspect we are going to get a wave of "why are my figures not interactive?" bug reports that trace back to the GUI wrappers installing conflicting input hooks.

tacaswell · 2018-10-31T20:09:05Z

but we will deal with that when it happens.

anntzer · 2018-11-01T00:19:54Z

Again, hopefully input hooks are only installed when the event loop is started, not when the package is imported.
Otherwise we'll have to resort to stuff to get the metadata about a backend (i.e. its event loop) without importing it; it's a bit a pain but not impossible (put that in a text file next to it with the same name and use the import machinery to find it without doing the import...).

ENH: allow matplotlib.use after getbackend

bd1646f

jklymak requested review from anntzer, efiring and tacaswell and removed request for efiring October 24, 2018 02:32

anntzer reviewed Oct 24, 2018

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anntzer approved these changes Oct 24, 2018

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anntzer reviewed Oct 24, 2018

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tacaswell modified the milestones: v3.1, v3.0.x Oct 24, 2018

DOC: fix docstring

52df902

DOC: API changes

c87e2da

tacaswell modified the milestones: v3.0.1, v3.0.x Oct 25, 2018

tacaswell merged commit 8c44c4d into matplotlib:master Oct 29, 2018

meeseeksmachine pushed a commit to meeseeksmachine/matplotlib that referenced this pull request Oct 29, 2018

Backport PR matplotlib#12608: ENH: allow matplotlib.use after getbackend

44b8bf7

meeseeksmachine mentioned this pull request Oct 29, 2018

Backport PR #12608 on branch v3.0.x (ENH: allow matplotlib.use after getbackend) #12666

Merged

jklymak added a commit that referenced this pull request Oct 29, 2018

Merge pull request #12666 from meeseeksmachine/auto-backport-of-pr-12…

4644c9f

…608-on-v3.0.x Backport PR #12608 on branch v3.0.x (ENH: allow matplotlib.use after getbackend)

jklymak deleted the enh-change-backend branch October 31, 2018 15:29

jklymak mentioned this pull request Oct 31, 2018

Warning: Cannot change to a different GUI toolkit: notebook. Using qt instead. #11365

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ENH: allow matplotlib.use after getbackend #12608

ENH: allow matplotlib.use after getbackend #12608

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ENH: allow matplotlib.use after getbackend #12608

ENH: allow matplotlib.use after getbackend #12608

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PR Summary

With this PR:

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