CODEWITHSUNDEEP
pythonmatplotlib
ravi
ravi

Reputation: 6328

AttributeError while trying to load the pickled matplotlib figure

I used pickle to dump matplotlib figure as shown in an answer in SO. Below is the code snippet-

import pickle
import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1,2,3],[10,-10,30])
pickle.dump(fig, open('fig.pickle', 'wb'))

Below is the code snippet to load the pickled figure-

import pickle
figx = pickle.load(open('fig.pickle', 'rb'))
figx.show()

The above code shows following error-

AttributeError: 'NoneType' object has no attribute 'manager'
Figure.show works only for figures managed by pyplot, normally created by pyplot.figure().

I am using Python 3.6.3 on Ubuntu 14.04 LTS 64 Bit OS. Below are the more details of my environment-

> import matplotlib
> matplotlib.__version__
'2.1.0'
> matplotlib.get_backend()
'Qt5Agg'
> import sys
> sys.version_info
sys.version_info(major=3, minor=6, micro=3, releaselevel='final', serial=0)

PS: My questions seem similar to this question asked at SO. However, it is different since the provided answer is not running and throwing exceptions.

Upvotes: 6

Views: 7331

Answers (3)

Lars-Christian Tokle
Lars-Christian Tokle

Reputation: 21

As pointed out in Nathan Kiners answer, you need a manager. However, you can create a manager from a figure. If you then set the manager to active, plt.show() will work on it.

Here is a function that does this

def show_fig_from_pickle(pickle_file, block_show=True):
    import pickle
    from matplotlib import _pylab_helpers
    import matplotlib.pyplot as plt
    with open(pickle_file, 'rb') as f:
        fig = pickle.load(f)
    
    # make sure plt has set a backend and get it
    bem = plt._get_backend_mod()
    # create a new figure manager for our figure
    mgr = bem.new_figure_manager_given_figure(num=fig.number, figure=fig)
    # set the new figure manager as active
    _pylab_helpers.Gcf.set_active(mgr)

    plt.show(block=block_show)
    return fig

See [pickleback][1] for registering pickle as a way to save figures. [1]: https://pypi.org/project/pickleback/

Upvotes: 1

Stever530
Stever530

Reputation: 29

The pyplot figure manager is needed to display the plot. You can create an instance and use the imported figure by doing this:

plt.new_figure_manager(1).canvas.figure = figx

Upvotes: -1

Nathan Kiner
Nathan Kiner

Reputation: 403

You need a canvas manager before you can show your figure. The same concept from question Matplotlib: how to show a figure that has been closed applies, you can create a function to make a dummy figure and steal its manager, as below (credit to Jean-Sébastien who wrote the answer above). 

def show_figure(fig):

    # create a dummy figure and use its
    # manager to display "fig"  
    dummy = plt.figure()
    new_manager = dummy.canvas.manager
    new_manager.canvas.figure = fig
    fig.set_canvas(new_manager.canvas)

With this function you can then run:

show_figure(figx)
figx.show()

Upvotes: 21

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