Trying to save an animated of graph with matplotlib in Python - "Invalid file object: <_io.BufferedReader name=76>"

I tried to save an animated graph by reproducing the code from this website. I then tried to reproduce a code from another website which was similar but got the same message error "Invalid file object: <_io.BufferedReader name=76>"

import numpy as np
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
import matplotlib.animation as animation


def update_line(num, data, line):
    line.set_data(data[..., :num])
    return line,

# Fixing random state for reproducibility
np.random.seed(19680801)


# Set up formatting for the movie files
Writer = animation.writers['ffmpeg']
writer = Writer(fps=15, metadata=dict(artist='Me'), bitrate=1800)


fig1 = plt.figure()

data = np.random.rand(2, 25)
l, = plt.plot([], [], 'r-')
plt.xlim(0, 1)
plt.ylim(0, 1)
plt.xlabel('x')
plt.title('test')
line_ani = animation.FuncAnimation(fig1, update_line, 25, fargs=(data, l),
                               interval=50, blit=True)
line_ani.save('lines.mp4', writer=writer)

fig2 = plt.figure()

x = np.arange(-9, 10)
y = np.arange(-9, 10).reshape(-1, 1)
base = np.hypot(x, y)
ims = []
for add in np.arange(15):
    ims.append((plt.pcolor(x, y, base + add, norm=plt.Normalize(0, 30)),))

im_ani = animation.ArtistAnimation(fig2, ims, interval=50, repeat_delay=3000,
                               blit=True)
im_ani.save('im.mp4', writer=writer)

and got the following error message:

/anaconda3/lib/python3.6/site-packages/ipykernel_launcher.py:3: UserWarning: 
This call to matplotlib.use() has no effect because the backend has already
been chosen; matplotlib.use() must be called *before* pylab, matplotlib.pyplot,
or matplotlib.backends is imported for the first time.

The backend was *originally* set to 'module://ipykernel.pylab.backend_inline' by the following code:
  File "/anaconda3/lib/python3.6/runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)
  File "/anaconda3/lib/python3.6/runpy.py", line 85, in _run_code
exec(code, run_globals)
  File "/anaconda3/lib/python3.6/site-packages/ipykernel_launcher.py", line 16, in <module>
app.launch_new_instance()
  File "/anaconda3/lib/python3.6/site-packages/traitlets/config/application.py", line 658, in launch_instance
app.start()
  File "/anaconda3/lib/python3.6/site-packages/ipykernel/kernelapp.py", line 486, in start
self.io_loop.start()
  File "/anaconda3/lib/python3.6/site-packages/tornado/platform/asyncio.py", line 127, in start
self.asyncio_loop.run_forever()
  File "/anaconda3/lib/python3.6/asyncio/base_events.py", line 422, in run_forever
self._run_once()
  File "/anaconda3/lib/python3.6/asyncio/base_events.py", line 1432, in _run_once
handle._run()
  File "/anaconda3/lib/python3.6/asyncio/events.py", line 145, in _run
self._callback(*self._args)
  File "/anaconda3/lib/python3.6/site-packages/tornado/platform/asyncio.py", line 117, in _handle_events
handler_func(fileobj, events)
  File "/anaconda3/lib/python3.6/site-packages/tornado/stack_context.py", line 276, in null_wrapper
return fn(*args, **kwargs)
  File "/anaconda3/lib/python3.6/site-packages/zmq/eventloop/zmqstream.py", line 450, in _handle_events
self._handle_recv()
  File "/anaconda3/lib/python3.6/site-packages/zmq/eventloop/zmqstream.py", line 480, in _handle_recv
self._run_callback(callback, msg)
  File "/anaconda3/lib/python3.6/site-packages/zmq/eventloop/zmqstream.py", line 432, in _run_callback
callback(*args, **kwargs)
  File "/anaconda3/lib/python3.6/site-packages/tornado/stack_context.py", line 276, in null_wrapper
return fn(*args, **kwargs)
  File "/anaconda3/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 283, in dispatcher
return self.dispatch_shell(stream, msg)
  File "/anaconda3/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 233, in dispatch_shell
handler(stream, idents, msg)
  File "/anaconda3/lib/python3.6/site-packages/ipykernel/kernelbase.py", line 399, in execute_request
user_expressions, allow_stdin)
  File "/anaconda3/lib/python3.6/site-packages/ipykernel/ipkernel.py", line 208, in do_execute
res = shell.run_cell(code, store_history=store_history, silent=silent)
  File "/anaconda3/lib/python3.6/site-packages/ipykernel/zmqshell.py", line 537, in run_cell
return super(ZMQInteractiveShell, self).run_cell(*args, **kwargs)
  File "/anaconda3/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 2666, in run_cell
self.events.trigger('post_run_cell', result)
  File "/anaconda3/lib/python3.6/site-packages/IPython/core/events.py", line 88, in trigger
func(*args, **kwargs)
  File "/anaconda3/lib/python3.6/site-packages/ipykernel/pylab/backend_inline.py", line 160, in configure_once
activate_matplotlib(backend)
  File "/anaconda3/lib/python3.6/site-packages/IPython/core/pylabtools.py", line 311, in activate_matplotlib
matplotlib.pyplot.switch_backend(backend)
  File "/anaconda3/lib/python3.6/site-packages/matplotlib/pyplot.py", line 229, in switch_backend
matplotlib.use(newbackend, warn=False, force=True)
  File "/anaconda3/lib/python3.6/site-packages/matplotlib/__init__.py", line 1305, in use
reload(sys.modules['matplotlib.backends'])
  File "/anaconda3/lib/python3.6/importlib/__init__.py", line 166, in reload
_bootstrap._exec(spec, module)
  File "/anaconda3/lib/python3.6/site-packages/matplotlib/backends/__init__.py", line 14, in <module>
line for line in traceback.format_stack()


      This is separate from the ipykernel package so we can avoid doing imports until
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-3-97bf2a96714e> in <module>()
 29 line_ani = animation.FuncAnimation(fig1, update_line, 25, fargs=(data, l),
 30                                    interval=50, blit=True)
---> 31 line_ani.save('lines.mp4', writer=writer)
 32 
 33 fig2 = plt.figure()

/anaconda3/lib/python3.6/site-packages/matplotlib/animation.py in save(self, filename, writer, fps, dpi, codec, bitrate, extra_args, metadata, extra_anim, savefig_kwargs)
   1258                         # TODO: See if turning off blit is really necessary
   1259                         anim._draw_next_frame(d, blit=False)
-> 1260                     writer.grab_frame(**savefig_kwargs)
   1261 
   1262         # Reconnect signal for first draw if necessary

/anaconda3/lib/python3.6/contextlib.py in __exit__(self, type, value, traceback)
     97                 value = type()
     98             try:
---> 99                 self.gen.throw(type, value, traceback)
    100             except StopIteration as exc:
    101                 # Suppress StopIteration *unless* it's the same exception that

/anaconda3/lib/python3.6/site-packages/matplotlib/animation.py in saving(self, fig, outfile, dpi, *args, **kwargs)
    235             yield self
    236         finally:
--> 237             self.finish()
    238 
    239 

/anaconda3/lib/python3.6/site-packages/matplotlib/animation.py in finish(self)
    367     def finish(self):
    368         '''Finish any processing for writing the movie.'''
--> 369         self.cleanup()
    370 
    371     def grab_frame(self, **savefig_kwargs):

/anaconda3/lib/python3.6/site-packages/matplotlib/animation.py in cleanup(self)
    406     def cleanup(self):
    407         '''Clean-up and collect the process used to write the movie file.'''
--> 408         out, err = self._proc.communicate()
    409         self._frame_sink().close()
    410         verbose.report('MovieWriter -- '

/anaconda3/lib/python3.6/subprocess.py in communicate(self, input, timeout)
    841 
    842             try:
--> 843                 stdout, stderr = self._communicate(input, endtime, timeout)
    844             finally:
    845                 self._communication_started = True

/anaconda3/lib/python3.6/subprocess.py in _communicate(self, input, endtime, orig_timeout)
   1503                     selector.register(self.stdin, selectors.EVENT_WRITE)
   1504                 if self.stdout:
-> 1505                     selector.register(self.stdout, selectors.EVENT_READ)
   1506                 if self.stderr:
   1507                     selector.register(self.stderr, selectors.EVENT_READ)

/anaconda3/lib/python3.6/selectors.py in register(self, fileobj, events, data)
    349 
    350         def register(self, fileobj, events, data=None):
--> 351             key = super().register(fileobj, events, data)
    352             poll_events = 0
    353             if events & EVENT_READ:

/anaconda3/lib/python3.6/selectors.py in register(self, fileobj, events, data)
    235             raise ValueError("Invalid events: {!r}".format(events))
    236 
--> 237         key = SelectorKey(fileobj, self._fileobj_lookup(fileobj), events, data)
    238 
    239         if key.fd in self._fd_to_key:

/anaconda3/lib/python3.6/selectors.py in _fileobj_lookup(self, fileobj)
    222         """
    223         try:
--> 224             return _fileobj_to_fd(fileobj)
    225         except ValueError:
    226             # Do an exhaustive search.

/anaconda3/lib/python3.6/selectors.py in _fileobj_to_fd(fileobj)
     37         except (AttributeError, TypeError, ValueError):
     38             raise ValueError("Invalid file object: "
---> 39                              "{!r}".format(fileobj)) from None
     40     if fd < 0:
     41         raise ValueError("Invalid file descriptor: {}".format(fd))

ValueError: Invalid file object: <_io.BufferedReader name=76>

I tried to run other codes available online for animated graph and got the same error. I updated the version of ffmpeg but it didn't help. What should I do?

In OSX I solved it by:

1) installing ffmpeg via brew

brew install ffmpeg

2) upgrade ffmpeg also via brew

brew upgrade ffmpeg

3) adding the path of "ffmpeg" just after "matplotlib":

# -*- coding: utf-8 -*-
"""
Created on Thu Oct 20 22:19:44 2018

@author: Irbin
"""

import numpy as np
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
import matplotlib.animation as animation
plt.rcParams['animation.ffmpeg_path'] = '/usr/local/bin/ffmpeg' # Add the path of ffmpeg here!!

def update_line(num, data, line):
    line.set_data(data[..., :num])
    return line,

# Fixing random state for reproducibility
np.random.seed(19680801)


# Set up formatting for the movie files
Writer = animation.writers['ffmpeg']
writer = Writer(fps=15, metadata=dict(artist='Me'), bitrate=1800)


fig1 = plt.figure()

data = np.random.rand(2, 25)
l, = plt.plot([], [], 'r-')
plt.xlim(0, 1)
plt.ylim(0, 1)
plt.xlabel('x')
plt.title('test')
line_ani = animation.FuncAnimation(fig1, update_line, 25, fargs=(data, l),
                                   interval=50, blit=True)
line_ani.save('lines.mp4', writer=writer)

fig2 = plt.figure()

x = np.arange(-9, 10)
y = np.arange(-9, 10).reshape(-1, 1)
base = np.hypot(x, y)
ims = []
for add in np.arange(15):
    ims.append((plt.pcolor(x, y, base + add, norm=plt.Normalize(0, 30)),))

im_ani = animation.ArtistAnimation(fig2, ims, interval=50, repeat_delay=3000,
                                   blit=True)
im_ani.save('im.mp4', writer=writer)

Be aware you can get an error if you change the output directory of your .mp4 file.