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Fix passing iterator as frames to FuncAnimation #13679

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Fix passing iterator as frames to FuncAnimation #13679

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22 changes: 22 additions & 0 deletions lib/matplotlib/animation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
import abc
import base64
import contextlib
import copy
from io import BytesIO, TextIOWrapper
import itertools
import logging
Expand Down Expand Up @@ -1545,6 +1546,14 @@ def func(frame, *fargs) -> iterable_of_artists
- If an iterable, then simply use the values provided. If the
iterable has a length, it will override the *save_count* kwarg.

Note that when using ``repeat=True`` (the default) *frames* must
be iterable multiple times. This is true for most common iterables.

However, e.g. generator expressions and possibly some custom classes
that implement the iterator protocol cannot be used. Technically, we
require either ``iter(frames) is not frames`` or *frames* must
support ``copy.copy(frames)``).

- If an integer, then equivalent to passing ``range(frames)``

- If a generator function, then must have the signature::
Expand Down Expand Up @@ -1623,6 +1632,19 @@ def __init__(self, fig, func, frames=None, init_func=None, fargs=None,
elif callable(frames):
self._iter_gen = frames
elif np.iterable(frames):
if iter(frames) is not frames or not kwargs.get('repeat', True):
self._iter_gen = lambda: iter(frames)
else:
# Since repeat=True we copy frames, to ensure that _iter_gen()
# returns a new iterator on each call.
try:
# Fail early if we cannot copy frames.
copy.copy(frames)
except TypeError:
raise ValueError(
'frames must be iterable multiple times if '
'repeat=True.')
self._iter_gen = lambda: iter(copy.copy(frames))
self._iter_gen = lambda: iter(frames)
if hasattr(frames, '__len__'):
self.save_count = len(frames)
Expand Down
7 changes: 7 additions & 0 deletions lib/matplotlib/tests/test_animation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,13 @@ def test_no_length_frames():
.save('unused.null', writer=NullMovieWriter()))


def test_generator_expression_repeat():
"""A generator expression cannot be used for frames if repeat=True"""
with pytest.raises(ValueError) as e:
make_animation(frames=(i for i in range(5)), repeat=True)
assert 'frames must be iterable multiple times' in str(e)


def test_movie_writer_registry():
ffmpeg_path = mpl.rcParams['animation.ffmpeg_path']
# Not sure about the first state as there could be some writer
Expand Down