animation freezes in Jupyter notebook with matplotlib-3.3

[johnomotani]

In a simple Jupyter notebook based on the parametric example, playback freezes when using matplotlib-3.3.2, using the latest release animatplot-0.4.1.

Notebook contained (sorry, Github won't let me attach a .ipynb):

%matplotlib notebook
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.animation import PillowWriter
import animatplot as amp


def psi(t):
    x = t
    y = np.sin(t)
    return x, y


t = np.linspace(0, 2*np.pi, 25)
x, y = psi(t)

X, Y = amp.util.parametric_line(x, y)

timeline = amp.Timeline(t, 's', 24)

ax = plt.axes(xlim=[0, 7], ylim=[-1.1, 1.1])
block1 = amp.blocks.Line(X, Y, ax=ax)
# or equivalently
# block1 = amp.blocks.ParametricLine(x, y, ax=ax)

anim = amp.Animation([block1], timeline)

# Your standard matplotlib stuff
plt.title('Parametric Line')
plt.xlabel('x')
plt.ylabel(r'y')

# Create Interactive Elements
anim.toggle()
anim.timeline_slider()

and freezes with the error

[IPKernelApp] WARNING | Unknown error in handling startup files:
ERROR:tornado.application:Exception in callback <bound method TimerBase._on_timer of <matplotlib.backends.backend_webagg_core.TimerTornado object at 0x7fd353719b50>>
Traceback (most recent call last):
  File ".../python3.7/site-packages/tornado/ioloop.py", line 907, in _run
    return self.callback()
  File ".../python3.7/site-packages/matplotlib/backend_bases.py", line 1194, in _on_timer
    ret = func(*args, **kwargs)
  File ".../python3.7/site-packages/matplotlib/animation.py", line 1432, in _step
    self.event_source.interval = self._repeat_delay
  File ".../python3.7/site-packages/matplotlib/backend_bases.py", line 1135, in interval
    self._timer_set_interval()
  File ".../python3.7/site-packages/matplotlib/backends/backend_webagg_core.py", line 537, in _timer_set_interval
    self._timer_start()
  File ".../python3.7/site-packages/matplotlib/backends/backend_webagg_core.py", line 520, in _timer_start
    self.interval)
  File ".../python3.7/site-packages/tornado/ioloop.py", line 873, in __init__
    raise ValueError("Periodic callback must have a positive callback_time")
ValueError: Periodic callback must have a positive callback_time

Animation worked as expected with matplotlib-3.2.2.

conda won't let me update just matplotlib from 3.2 to 3.3. Don't understand why, but it complained about package conflicts. So a few apparently unrelated packages had different versions in the environments I tested with. Output of conda env export below.
For matplotlib-3.2:

name: animatplot-test-matplotlib-3.2a
channels:
  - conda-forge
  - defaults
dependencies:
  - _libgcc_mutex=0.1=conda_forge
  - _openmp_mutex=4.5=1_gnu
  - animatplot=0.4.1=py_0
  - argon2-cffi=20.1.0=py37h8f50634_1
  - async_generator=1.10=py_0
  - attrs=20.2.0=pyh9f0ad1d_0
  - backports=1.0=py_2
  - backports.functools_lru_cache=1.6.1=py_0
  - bleach=3.2.1=pyh9f0ad1d_0
  - ca-certificates=2020.6.20=hecda079_0
  - certifi=2020.6.20=py37hc8dfbb8_0
  - cffi=1.14.3=py37h2b28604_0
  - cycler=0.10.0=py_2
  - dbus=1.13.6=he372182_0
  - decorator=4.4.2=py_0
  - defusedxml=0.6.0=py_0
  - entrypoints=0.3=py37hc8dfbb8_1001
  - expat=2.2.9=he1b5a44_2
  - fontconfig=2.13.1=h86ecdb6_1001
  - freetype=2.10.2=he06d7ca_0
  - gettext=0.19.8.1=hc5be6a0_1002
  - glib=2.66.0=h0dae87d_0
  - gst-plugins-base=1.14.5=h0935bb2_2
  - gstreamer=1.14.5=h36ae1b5_2
  - icu=64.2=he1b5a44_1
  - importlib-metadata=2.0.0=py37hc8dfbb8_0
  - importlib_metadata=2.0.0=0
  - ipykernel=5.3.4=py37h43977f1_0
  - ipython=5.8.0=py37_1
  - ipython_genutils=0.2.0=py_1
  - ipywidgets=7.5.1=pyh9f0ad1d_1
  - jinja2=2.11.2=pyh9f0ad1d_0
  - jpeg=9d=h516909a_0
  - jsonschema=3.2.0=py37hc8dfbb8_1
  - jupyter=1.0.0=py_2
  - jupyter_client=6.1.7=py_0
  - jupyter_console=5.2.0=py37_1
  - jupyter_core=4.6.3=py37hc8dfbb8_1
  - jupyterlab_pygments=0.1.1=pyh9f0ad1d_0
  - kiwisolver=1.2.0=py37h99015e2_0
  - ld_impl_linux-64=2.35=h769bd43_9
  - libblas=3.8.0=17_openblas
  - libcblas=3.8.0=17_openblas
  - libclang=9.0.1=default_hde54327_0
  - libffi=3.2.1=he1b5a44_1007
  - libgcc-ng=9.3.0=h24d8f2e_16
  - libgfortran-ng=7.5.0=hdf63c60_16
  - libgomp=9.3.0=h24d8f2e_16
  - libiconv=1.16=h516909a_0
  - liblapack=3.8.0=17_openblas
  - libllvm9=9.0.1=he513fc3_1
  - libopenblas=0.3.10=pthreads_hb3c22a3_4
  - libpng=1.6.37=hed695b0_2
  - libsodium=1.0.18=h516909a_0
  - libstdcxx-ng=9.3.0=hdf63c60_16
  - libuuid=2.32.1=h14c3975_1000
  - libxcb=1.13=h14c3975_1002
  - libxkbcommon=0.10.0=he1b5a44_0
  - libxml2=2.9.10=hee79883_0
  - markupsafe=1.1.1=py37h8f50634_1
  - matplotlib=3.2.2=1
  - matplotlib-base=3.2.2=py37h30547a4_0
  - mistune=0.8.4=py37h8f50634_1001
  - nbclient=0.5.0=py_0
  - nbconvert=6.0.6=py37hc8dfbb8_0
  - nbformat=5.0.7=py_0
  - ncurses=6.2=he1b5a44_1
  - nest-asyncio=1.4.0=py_1
  - notebook=6.1.4=py37hc8dfbb8_0
  - nspr=4.29=he1b5a44_0
  - nss=3.57=he751ad9_0
  - numpy=1.19.1=py37h7ea13bd_2
  - openssl=1.1.1h=h516909a_0
  - packaging=20.4=pyh9f0ad1d_0
  - pandoc=2.10.1=h516909a_0
  - pandocfilters=1.4.2=py_1
  - pcre=8.44=he1b5a44_0
  - pexpect=4.8.0=py37hc8dfbb8_1
  - pickleshare=0.7.5=py37hc8dfbb8_1001
  - pip=20.2.3=py_0
  - prometheus_client=0.8.0=pyh9f0ad1d_0
  - prompt_toolkit=1.0.15=py_1
  - pthread-stubs=0.4=h14c3975_1001
  - ptyprocess=0.6.0=py_1001
  - pycparser=2.20=pyh9f0ad1d_2
  - pygments=2.7.1=py_0
  - pyparsing=2.4.7=pyh9f0ad1d_0
  - pyqt=5.12.3=py37h8685d9f_3
  - pyrsistent=0.17.3=py37h8f50634_0
  - python=3.7.8=h6f2ec95_1_cpython
  - python-dateutil=2.8.1=py_0
  - python_abi=3.7=1_cp37m
  - pyzmq=19.0.2=py37hac76be4_0
  - qt=5.12.5=hd8c4c69_1
  - qtconsole=4.7.7=pyh9f0ad1d_0
  - qtpy=1.9.0=py_0
  - readline=8.0=he28a2e2_2
  - send2trash=1.5.0=py_0
  - setuptools=49.6.0=py37hc8dfbb8_1
  - simplegeneric=0.8.1=py_1
  - six=1.15.0=pyh9f0ad1d_0
  - sqlite=3.33.0=h4cf870e_0
  - terminado=0.9.1=py37hc8dfbb8_0
  - testpath=0.4.4=py_0
  - tk=8.6.10=hed695b0_0
  - tornado=6.0.4=py37h8f50634_1
  - traitlets=5.0.4=py_0
  - wcwidth=0.2.5=pyh9f0ad1d_1
  - webencodings=0.5.1=py_1
  - wheel=0.35.1=pyh9f0ad1d_0
  - widgetsnbextension=3.5.1=py37hc8dfbb8_1
  - xorg-libxau=1.0.9=h14c3975_0
  - xorg-libxdmcp=1.1.3=h516909a_0
  - xz=5.2.5=h516909a_1
  - zeromq=4.3.2=he1b5a44_3
  - zipp=3.2.0=py_0
  - zlib=1.2.11=h516909a_1009
  - pip:
    - pyqt5-sip==4.19.18
    - pyqtchart==5.12
    - pyqtwebengine==5.12.1
prefix: .../envs/animatplot-test-matplotlib-3.2a

and for matplotlib-3.3:

name: animatplot-test-matplotlib-3.3b
channels:
  - conda-forge
  - defaults
dependencies:
  - _libgcc_mutex=0.1=conda_forge
  - _openmp_mutex=4.5=1_gnu
  - animatplot=0.4.1=py_0
  - argon2-cffi=20.1.0=py37h8f50634_1
  - async_generator=1.10=py_0
  - attrs=20.2.0=pyh9f0ad1d_0
  - backports=1.0=py_2
  - backports.functools_lru_cache=1.6.1=py_0
  - bleach=3.2.1=pyh9f0ad1d_0
  - ca-certificates=2020.6.20=hecda079_0
  - certifi=2020.6.20=py37hc8dfbb8_0
  - cffi=1.14.3=py37h2b28604_0
  - cycler=0.10.0=py_2
  - dbus=1.13.6=he372182_0
  - decorator=4.4.2=py_0
  - defusedxml=0.6.0=py_0
  - entrypoints=0.3=py37hc8dfbb8_1001
  - expat=2.2.9=he1b5a44_2
  - fontconfig=2.13.1=h1056068_1002
  - freetype=2.10.2=he06d7ca_0
  - gettext=0.19.8.1=hc5be6a0_1002
  - glib=2.66.0=h0dae87d_0
  - gst-plugins-base=1.14.5=h0935bb2_2
  - gstreamer=1.14.5=h36ae1b5_2
  - icu=67.1=he1b5a44_0
  - importlib-metadata=2.0.0=py37hc8dfbb8_0
  - importlib_metadata=2.0.0=0
  - ipykernel=5.3.4=py37h43977f1_0
  - ipython=5.8.0=py37_1
  - ipython_genutils=0.2.0=py_1
  - ipywidgets=7.5.1=pyh9f0ad1d_1
  - jinja2=2.11.2=pyh9f0ad1d_0
  - jpeg=9d=h516909a_0
  - jsonschema=3.2.0=py37hc8dfbb8_1
  - jupyter=1.0.0=py_2
  - jupyter_client=6.1.7=py_0
  - jupyter_console=5.2.0=py37_1
  - jupyter_core=4.6.3=py37hc8dfbb8_1
  - jupyterlab_pygments=0.1.1=pyh9f0ad1d_0
  - kiwisolver=1.2.0=py37h99015e2_0
  - krb5=1.17.1=hfafb76e_3
  - lcms2=2.11=hbd6801e_0
  - ld_impl_linux-64=2.35=h769bd43_9
  - libblas=3.8.0=17_openblas
  - libcblas=3.8.0=17_openblas
  - libclang=10.0.1=default_hde54327_1
  - libedit=3.1.20191231=he28a2e2_2
  - libevent=2.1.10=hcdb4288_2
  - libffi=3.2.1=he1b5a44_1007
  - libgcc-ng=9.3.0=h24d8f2e_16
  - libgfortran-ng=7.5.0=hdf63c60_16
  - libgomp=9.3.0=h24d8f2e_16
  - libiconv=1.16=h516909a_0
  - liblapack=3.8.0=17_openblas
  - libllvm10=10.0.1=he513fc3_3
  - libopenblas=0.3.10=pthreads_hb3c22a3_4
  - libpng=1.6.37=hed695b0_2
  - libpq=12.3=h5513abc_0
  - libsodium=1.0.18=h516909a_0
  - libstdcxx-ng=9.3.0=hdf63c60_16
  - libtiff=4.1.0=hc7e4089_6
  - libuuid=2.32.1=h14c3975_1000
  - libwebp-base=1.1.0=h516909a_3
  - libxcb=1.13=h14c3975_1002
  - libxkbcommon=0.10.0=he1b5a44_0
  - libxml2=2.9.10=h68273f3_2
  - lz4-c=1.9.2=he1b5a44_3
  - markupsafe=1.1.1=py37h8f50634_1
  - matplotlib=3.3.2=0
  - matplotlib-base=3.3.2=py37hd478181_0
  - mistune=0.8.4=py37h8f50634_1001
  - mysql-common=8.0.21=2
  - mysql-libs=8.0.21=hf3661c5_2
  - nbclient=0.5.0=py_0
  - nbconvert=6.0.6=py37hc8dfbb8_0
  - nbformat=5.0.7=py_0
  - ncurses=6.2=he1b5a44_1
  - nest-asyncio=1.4.0=py_1
  - notebook=6.1.4=py37hc8dfbb8_0
  - nspr=4.29=he1b5a44_0
  - nss=3.57=he751ad9_0
  - numpy=1.19.1=py37h7ea13bd_2
  - olefile=0.46=py_0
  - openssl=1.1.1h=h516909a_0
  - packaging=20.4=pyh9f0ad1d_0
  - pandoc=2.10.1=h516909a_0
  - pandocfilters=1.4.2=py_1
  - pcre=8.44=he1b5a44_0
  - pexpect=4.8.0=py37hc8dfbb8_1
  - pickleshare=0.7.5=py37hc8dfbb8_1001
  - pillow=7.2.0=py37h718be6c_1
  - pip=20.2.3=py_0
  - prometheus_client=0.8.0=pyh9f0ad1d_0
  - prompt_toolkit=1.0.15=py_1
  - pthread-stubs=0.4=h14c3975_1001
  - ptyprocess=0.6.0=py_1001
  - pycparser=2.20=pyh9f0ad1d_2
  - pygments=2.7.1=py_0
  - pyparsing=2.4.7=pyh9f0ad1d_0
  - pyqt=5.12.3=py37h8685d9f_3
  - pyrsistent=0.17.3=py37h8f50634_0
  - python=3.7.8=h6f2ec95_1_cpython
  - python-dateutil=2.8.1=py_0
  - python_abi=3.7=1_cp37m
  - pyzmq=19.0.2=py37hac76be4_0
  - qt=5.12.9=h1f2b2cb_0
  - qtconsole=4.7.7=pyh9f0ad1d_0
  - qtpy=1.9.0=py_0
  - readline=8.0=he28a2e2_2
  - send2trash=1.5.0=py_0
  - setuptools=49.6.0=py37hc8dfbb8_1
  - simplegeneric=0.8.1=py_1
  - six=1.15.0=pyh9f0ad1d_0
  - sqlite=3.33.0=h4cf870e_0
  - terminado=0.9.1=py37hc8dfbb8_0
  - testpath=0.4.4=py_0
  - tk=8.6.10=hed695b0_0
  - tornado=6.0.4=py37h8f50634_1
  - traitlets=5.0.4=py_0
  - wcwidth=0.2.5=pyh9f0ad1d_1
  - webencodings=0.5.1=py_1
  - wheel=0.35.1=pyh9f0ad1d_0
  - widgetsnbextension=3.5.1=py37hc8dfbb8_1
  - xorg-libxau=1.0.9=h14c3975_0
  - xorg-libxdmcp=1.1.3=h516909a_0
  - xz=5.2.5=h516909a_1
  - zeromq=4.3.2=he1b5a44_3
  - zipp=3.2.0=py_0
  - zlib=1.2.11=h516909a_1009
  - zstd=1.4.5=h6597ccf_2
  - pip:
    - pyqt5-sip==4.19.18
    - pyqtchart==5.12
    - pyqtwebengine==5.12.1
prefix: .../envs/animatplot-test-matplotlib-3.3b

[johnomotani]

This was a matplotlib issue matplotlib/matplotlib#18580, and was fixed in matplotlib-3.3.3.