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Warn if an animation is gc'd before doing anything. #18445

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Merged
merged 1 commit into from
Sep 11, 2020
Merged

Warn if an animation is gc'd before doing anything. #18445

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15 changes: 14 additions & 1 deletion lib/matplotlib/animation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
import sys
from tempfile import TemporaryDirectory
import uuid
import warnings

import numpy as np

Expand Down Expand Up @@ -907,6 +908,8 @@ class Animation:
"""

def __init__(self, fig, event_source=None, blit=False):
self._draw_was_started = False

self._fig = fig
# Disables blitting for backends that don't support it. This
# allows users to request it if available, but still have a
Expand All @@ -931,6 +934,14 @@ def __init__(self, fig, event_source=None, blit=False):
if self._blit:
self._setup_blit()

def __del__(self):
if not getattr(self, '_draw_was_started', True):
warnings.warn(
'Animation was deleted without rendering anything. This is '
'most likely unintended. To prevent deletion, assign the '
'Animation to a variable that exists for as long as you need '
'the Animation.')

def _start(self, *args):
"""
Starts interactive animation. Adds the draw frame command to the GUI
Expand Down Expand Up @@ -1166,7 +1177,7 @@ def _draw_next_frame(self, framedata, blit):
def _init_draw(self):
# Initial draw to clear the frame. Also used by the blitting code
# when a clean base is required.
pass
self._draw_was_started = True

def _pre_draw(self, framedata, blit):
# Perform any cleaning or whatnot before the drawing of the frame.
Expand Down Expand Up @@ -1484,6 +1495,7 @@ def __init__(self, fig, artists, *args, **kwargs):
super().__init__(fig, *args, **kwargs)

def _init_draw(self):
super()._init_draw()
# Make all the artists involved in *any* frame invisible
figs = set()
for f in self.new_frame_seq():
Expand Down Expand Up @@ -1695,6 +1707,7 @@ def gen():
return gen()

def _init_draw(self):
super()._init_draw()
# Initialize the drawing either using the given init_func or by
# calling the draw function with the first item of the frame sequence.
# For blitting, the init_func should return a sequence of modified
Expand Down
9 changes: 9 additions & 0 deletions lib/matplotlib/tests/test_animation.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import gc
import os
from pathlib import Path
import subprocess
Expand Down Expand Up @@ -75,6 +76,14 @@ def test_null_movie_writer():
assert writer._count == num_frames


def test_animation_delete():
anim = make_animation(frames=5)

with pytest.warns(Warning, match='Animation was deleted'):
del anim
gc.collect()


def test_movie_writer_dpi_default():
class DummyMovieWriter(animation.MovieWriter):
def _run(self):
Expand Down