8000 Merge pull request #5454 from WarrenWeckesser/abstract-movie-writer · matplotlib/matplotlib@a4aebe3 · GitHub
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Merge pull request #5454 from WarrenWeckesser/abstract-movie-writer
ENH: Create an abstract base class for movie writers.
2 parents 723d015 + 6bae745 commit a4aebe3

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‎doc/users/whats_new/abstract_movie_writer.rst

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Abstract base class for movie writers
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-------------------------------------
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The new :class:`~matplotlib.animation.AbstractMovieWriter` class defines
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the API required by a class that is to be used as the `writer` in the
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`save` method of the :class:`~matplotlib.animation.Animation` class.
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The existing :class:`~matplotlib.animation.MovieWriter` class now derives
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from the new abstract base class.

‎lib/matplotlib/animation.py

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except ImportError:
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# python2
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from base64 import encodestring as encodebytes
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import abc
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import contextlib
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import tempfile
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from matplotlib.cbook import iterable, is_string_like
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writers = MovieWriterRegistry()
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class MovieWriter(object):
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class AbstractMovieWriter(six.with_metaclass(abc.ABCMeta)):
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'''
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Abstract base class for writing movies. Fundamentally, what a MovieWriter
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does is provide is a way to grab frames by calling grab_frame().
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setup() is called to start the process and finish() is called afterwards.
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This class is set up to provide for writing movie frame data to a pipe.
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saving() is provided as a context manager to facilitate this process as::
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with moviewriter.saving(fig, outfile='myfile.mp4', dpi=100):
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# Iterate over frames
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moviewriter.grab_frame(**savefig_kwargs)
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The use of the context manager ensures that setup() and finish() are
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performed as necessary.
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An instance of a concrete subclass of this class can be given as the
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`writer` argument of `Animation.save()`.
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'''
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@abc.abstractmethod
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def setup(self, fig, outfile, dpi, *args):
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'''
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Perform setup for writing the movie file.
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fig: `matplotlib.Figure` instance
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The figure object that contains the information for frames
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outfile: string
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The filename of the resulting movie file
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dpi: int
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The DPI (or resolution) for the file. This controls the size
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in pixels of the resulting movie file.
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'''
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@abc.abstractmethod
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def grab_frame(self, **savefig_kwargs):
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'''
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Grab the image information from the figure and save as a movie frame.
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All keyword arguments in savefig_kwargs are passed on to the 'savefig'
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command that saves the figure.
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'''
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@abc.abstractmethod
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def finish(self):
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'Finish any processing for writing the movie.'
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@contextlib.contextmanager
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def saving(self, fig, outfile, dpi, *args):
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'''
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Context manager to facilitate writing the movie file.
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All arguments are passed on to `setup`.
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'''
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self.setup(fig, outfile, dpi, *args)
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yield
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self.finish()
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class MovieWriter(AbstractMovieWriter):
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'''
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Base class for writing movies. Fundamentally, what a MovieWriter does
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is provide is a way to grab frames by calling grab_frame(). setup()
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is called to start the process and finish() is called afterwards.
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This class is set up to provide for writing movie frame data to a pipe.
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saving() is provided as a context manager to facilitate this process as::
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with moviewriter.saving('myfile.mp4'):
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with moviewriter.saving(fig, outfile='myfile.mp4', dpi=100):
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# Iterate over frames
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moviewriter.grab_frame()
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moviewriter.grab_frame(**savefig_kwargs)
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The use of the context manager ensures that setup and cleanup are
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performed as necessary.
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# eliminates the need for temp files.
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self._run()
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@contextlib.contextmanager
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def saving(self, *args):
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'''
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Context manager to facilitate writing the movie file.
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``*args`` are any parameters that should be passed to `setup`.
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'''
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# This particular sequence is what contextlib.contextmanager wants
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self.setup(*args)
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yield
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self.finish()
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def _run(self):
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# Uses subprocess to call the program for assembling frames into a
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# movie file. *args* returns the sequence of command line arguments
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*filename* is the output filename, e.g., :file:`mymovie.mp4`
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*writer* is either an instance of :class:`MovieWriter` or a string
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key that identifies a class to use, such as 'ffmpeg' or 'mencoder'.
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If nothing is passed, the value of the rcparam `animation.writer` is
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used.
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*writer* is either an instance of :class:`AbstractMovieWriter` or
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a string key that identifies a class to use, such as 'ffmpeg' or
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'mencoder'. If nothing is passed, the value of the rcparam
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`animation.writer` is used.
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*fps* is the frames per second in the movie. Defaults to None,
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which will use the animation's specified interval to set the frames

‎lib/matplotlib/tests/test_animation.py

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import os
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import tempfile
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import numpy as np
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from numpy.testing import assert_equal
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from nose import with_setup
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from matplotlib import pyplot as plt
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from matplotlib import animation
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from matplotlib.testing.decorators import CleanupTest
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class NullMovieWriter(animation.AbstractMovieWriter):
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"""
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A minimal MovieWriter. It doesn't actually write anything.
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It just saves the arguments that were given to the setup() and
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grab_frame() methods as attributes, and counts how many times
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grab_frame() is called.
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This class doesn't have an __init__ method with the appropriate
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signature, and it doesn't define an isAvailable() method, so
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it cannot be added to the 'writers' registry.
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"""
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def setup(self, fig, outfile, dpi, *args):
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self.fig = fig
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self.outfile = outfile
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self.dpi = dpi
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self.args = args
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self._count = 0
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def grab_frame(self, **savefig_kwargs):
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self.savefig_kwargs = savefig_kwargs
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self._count += 1
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def finish(self):
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pass
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def test_null_movie_writer():
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# Test running an animation with NullMovieWriter.
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fig = plt.figure()
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def init():
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pass
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def animate(i):
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pass
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num_frames = 5
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filename = "unused.null"
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fps = 30
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dpi = 50
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savefig_kwargs = dict(foo=0)
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anim = animation.FuncAnimation(fig, animate, init_func=init,
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frames=num_frames)
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writer = NullMovieWriter()
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anim.save(filename, fps=fps, dpi=dpi, writer=writer,
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savefig_kwargs=savefig_kwargs)
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assert_equal(writer.fig, fig)
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assert_equal(writer.outfile, filename)
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assert_equal(writer.dpi, dpi)
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assert_equal(writer.args, ())
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assert_equal(writer.savefig_kwargs, savefig_kwargs)
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assert_equal(writer._count, num_frames)
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@animation.writers.register('null')
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class RegisteredNullMovieWriter(NullMovieWriter):
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# To be able to add NullMovieWriter to the 'writers' registry,
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# we must define an __init__ method with a specific signature,
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# and we must define the class method isAvailable().
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# (These methods are not actually required to use an instance
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# of this class as the 'writer' argument of Animation.save().)
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def __init__(self, fps=None, codec=None, bitrate=None,
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extra_args=None, metadata=None):
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pass
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@classmethod
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def isAvailable(self):
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return True
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WRITER_OUTPUT = dict(ffmpeg='mp4', ffmpeg_file='mp4',
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mencoder='mp4', mencoder_file='mp4',
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avconv='mp4', avconv_file='mp4',
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imagemagick='gif', imagemagick_file='gif')
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imagemagick='gif', imagemagick_file='gif',
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null='null')
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# Smoke test for saving animations. In the future, we should probably

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