tornado now a requirement?

[jankatins]

If I explicitly use a different backend, IMO the nbagg backend shouldn't be loaded.

C:\portabel\miniconda\envs\katins2\lib\site-packages\matplotlib\__init__.py:1355: 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.

  warnings.warn(_use_error_msg)
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-3-1fdbaaa8856e> in <module>()
      2 import matplotlib as mpl
      3 mpl.use('Agg')
----> 4 import matplotlib.pyplot as plt
      5 import matplotlib.animation as animation
      6 def updatefig(i):

C:\portabel\miniconda\envs\katins2\lib\site-packages\matplotlib\pyplot.py in <module>()
    112 
    113 from matplotlib.backends import pylab_setup
--> 114 _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
    115 
    116 _IP_REGISTERED = None

C:\portabel\miniconda\envs\katins2\lib\site-packages\matplotlib\backends\__init__.pyc in pylab_setup()
     30     # imports. 0 means only perform absolute imports.
     31     backend_mod = __import__(backend_name,
---> 32                              globals(),locals(),[backend_name],0)
     33 
     34     # Things we pull in from all backends

C:\portabel\miniconda\envs\katins2\lib\site-packages\matplotlib\backends\backend_nbagg.py in <module>()
     12 from uuid import uuid4 as uuid
     13 
---> 14 import tornado.ioloop
     15 
     16 from IPython.display import display, Javascript, HTML

ImportError: No module named tornado.ioloop

[tacaswell]

It looks like matplotlib.backends is getting imported by something before you can call use so it is having no effect. Can you try passing force=True into use.

[jankatins]

Ok, I tried to reproduce it and I couldn't: If I set agg, it loads the agg backend and not nbagg:

from sys import modules
import matplotlib
matplotlib.use('Agg')
middle = sorted([x for x in modules.keys() if x.startswith("matplotlib.bac")])
import matplotlib.pylab as plt
last = sorted([x for x in modules.keys() if x.startswith("matplotlib.bac")])

diff = set(last) - set(middle)
print(middle) # empty
print(diff) # only the agg backends

-> closing and sorry for the noise...

[jankatins]

Ok I think I got it:

first cell included a :

%matplotlib notebook

-> I got an error about tornado, removed the line and then executed the cell with the mpl.use("agg"). -> it cached the backend name from the matplotlib notebook call to mpl.use() and now you can't reset it.

Not sure if there is a case for "if the backend init/loading didn't work, remove the cached backend name from use(...)? Or let use() overwrite if the backend isn't in fact initialized? Similar to this:

import matplotlib
matplotlib.use('nbAgg')
matplotlib.use('Agg')
import matplotlib.pyplot # works because backend is now agg

import matplotlib
matplotlib.use('nbAgg')
try:
    import matplotlib.pyplot
except ImportError:
    matplotlib.use('Agg') # gives a warning but no backend is yet loaded... 
    import matplotlib.pyplot # does not work...