10000 Figure is unpicklable after `savefig` · Issue #6870 · matplotlib/matplotlib · GitHub
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Kojoley opened this issue Jul 31, 2016 · 7 comments
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Figure is unpicklable after savefig #6870

Kojoley opened this issue Jul 31, 2016 · 7 comments
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v2.0.0

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@Kojoley
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Kojoley commented Jul 31, 2016 •
edited by QuLogic
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import matplotlib.pyplot as plt
import pickle
from io import BytesIO

def test_pickle_after_savefig():
    fig = plt.figure()
    fig.add_subplot(111)
    for fmt in ['pdf', 'png', 'svg']:
        fig.savefig(BytesIO(), format=fmt)
        try:
            pickle.dump(fig, BytesIO())
        except:
            print('Unpickable after "%s"' % fmt)
            raise

test_pickle_after_savefig()
>python test_pickle_after_savefig.py
Unpickable after "svg"
Traceback (most recent call last):
  File "test_pickle_after_savefig.py", line 16, in <module>
    test_pickle_after_savefig()
  File "test_pickle_after_savefig.py", line 11, in test_pickle_after_savefig
    pickle.dump(fig, BytesIO())
TypeError: cannot serialize '_io.TextIOWrapper' object

I think those warnings from pytest are maybe related:

>py.test -n 4 lib/matplotlib/tests/test_backend_svg.py::test_fill_black_with_alpha
============================= test session starts =============================
platform win32 -- Python 3.5.2, pytest-2.9.2, py-1.4.31, pluggy-0.3.1
rootdir: C:\Working\Repositories\matplotlib, inifile: pytest.ini
plugins: xdist-1.14
gw0 [1] / gw1 [1] / gw2 [1] / gw3 [1]
scheduling tests via LoadScheduling
.sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name=0 mode='r' encoding='cp866'>
sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name=1 mode='w' encoding='cp866'>
sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name=0 mode='r' encoding='cp866'>
sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name=0 mode='r' encoding='cp866'>
sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name=1 mode='w' encoding='cp866'>
sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name=1 mode='w' encoding='cp866'>
sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name=0 mode='r' encoding='cp866'>
sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name=1 mode='w' encoding='cp866'>

With a file name pickle fails in the pdf backend (and svg too):

import matplotlib.pylab as plt
import pickle
from io import BytesIO

def test_pickle_after_savefig2():
    fig = plt.figure()
    fig.add_subplot(111)
    for fmt in ['pdf', 'png', 'svg']:
        fig.savefig('test.%s' % fmt, format=fmt)
        try:
            pickle.dump(fig, BytesIO())
        except:
            print('Unpickable format is "%s"' % fmt)
            raise

test_pickle_after_savefig2()
>python test_pickle_after_savefig2.py
Unpickable format is "pdf"
Traceback (most recent call last):
  File "test_pickle_after_savefig2.py", line 16, in <module>
    test_pickle_after_savefig()
  File "test_pickle_after_savefig2.py", line 11, in test_pickle_after_savefig
    pickle.dump(fig, BytesIO())
TypeError: cannot serialize '_io.BufferedWriter' object
@dopplershift dopplershift changed the title Figure is unpickable after savefig Figure is unpicklable after savefig Jul 31, 2016
@Kojoley
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Kojoley commented Jul 31, 2016 •
edited
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I have tracked down the problem in the svg backend. XMLWriter (locates in fig._cachedRenderer._renderer.writer) keeps reference to the file object. The easiest solution is to add self.writer = None or del self.writer to the RendererSVG.finalize here, but I still do not know if it is the right solution.

@tacaswell
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The way we have solved this in other places in the codebase is to customize __getstate__ and __setstate__ on the objects that have non-pickable children.

@Kojoley
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Kojoley commented Aug 1, 2016

But then that warning from pytest will not be solved.

@tacaswell tacaswell added this to the 2.0.1 (next bug fix release) milestone Aug 1, 2016
@Kojoley
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Kojoley commented Aug 1, 2016

I see not reason why renderer should have reference to the file object passed to savefig

@Kojoley Kojoley mentioned this issue Aug 3, 2016
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@tacaswell
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Yes, you are correct, we should drop the reference to the file object in in the finalize step.

@jrbrodie77
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jrbrodie77 commented Sep 22, 2016 •
edited by tacaswell
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UPDATED: I meant to post this comment on #6899 (which is related to this issue)
I was just getting ready to create an issue with test cases. I'm seeing savefig side effects with 2.0.0b4
Is this fix in that version?

@Kojoley
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Kojoley commented Sep 22, 2016

I'm seeing savefig side effects with 2.0.0b4

Then you are commenting on a wrong issue.

QuLogic added a commit to QuLogic/matplotlib that referenced this issue Oct 22, 2016
@QuLogic
Don't pickle Axes' cached renderer.
7fe52ac 
It's not allowed to be pickled on a Figure, so presumably it shouldn't
be allowed on the Axes either.

Fixes matplotlib#6870.
Fixes matplotlib#6181.
Fixes matplotlib#3899.
@QuLogic QuLogic mentioned this issue Oct 22, 2016
Merged
@QuLogic QuLogic closed this as completed in 519b050 Nov 1, 2016
bcongdon pushed a commit to bcongdon/matplotlib that referenced this issue Nov 8, 2016
@QuLogic @bcongdon
Don't pickle Axes' cached renderer.
548d120 
It's not allowed to be pickled on a Figure, so presumably it shouldn't
be allowed on the Axes either.

Fixes matplotlib#6870.
Fixes matplotlib#6181.
Fixes matplotlib#3899.
bcongdon pushed a commit to bcongdon/matplotlib that referenced this issue Nov 8, 2016
@QuLogic @bcongdon
Don't pickle Axes' cached renderer.
0505585 
It's not allowed to be pickled on a Figure, so presumably it shouldn't
be allowed on the Axes either.

Fixes matplotlib#6870.
Fixes matplotlib#6181.
Fixes matplotlib#3899.
@QuLogic QuLogic modified the milestones: 2.0 (style change major release), 2.0.1 (next bug fix release) Dec 7, 2016
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