python - Pickle figures from matplotlib

Question

I am trying to recreate the simple pickle figure example from the question: Saving interactive Matplotlib figures, which is also sourced from Saving Matplotlib Figures Using Pickle. However, when I run the given codes the figures seems to pickle OK, but then I get an error when I try to load the pickled figure. I am running it using Canopy Enthought (v1.6.2.3262), using Matplotlib 1.5.1-1 and Numpy 1.9.2-3 on Python 2.7.3-1. The pickle code is:`

import numpy as np
import matplotlib.pyplot as plt
import pickle as pl

# Plot simple sinus function
fig_handle = plt.figure()
x = np.linspace(0,2*np.pi)
y = np.sin(x)
plt.plot(x,y)

# Save figure handle to disk
pl.dump(fig_handle,file('sinus.pickle','w'))`

The code to load the figure is:

import matplotlib.pyplot as plt
import pickle as pl
import numpy as np

# Load figure from disk and display
fig_handle = pl.load(open('sinus.pickle','rb'))
fig_handle.show()

and the error I get is:

%run "Z:EFNHigh_Resshow_picklefig.py"
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
Z:EFNHigh_Resshow_picklefig.py in <module>()
      4 
      5 #plot simple sinus function
----> 6 fig_handle = pl.load(open('Z:EFNHigh_Ressinus.pickle','rb'))
      7 fig_handle.show()

C:UsersTomAppDataLocalEnthoughtCanopyAppappdatacanopy-1.6.2.3262.win-x86_64libpickle.pyc in load(file)
   1376 
   1377 def load(file):
-> 1378     return Unpickler(file).load()
   1379 
   1380 def loads(str):

C:UsersTomAppDataLocalEnthoughtCanopyAppappdatacanopy-1.6.2.3262.win-x86_64libpickle.pyc in load(self)
    856             while 1:
    857                 key = read(1)
--> 858                 dispatch[key](self)
    859         except _Stop, stopinst:
    860             return stopinst.value

C:UsersTomAppDataLocalEnthoughtCanopyAppappdatacanopy-1.6.2.3262.win-x86_64libpickle.pyc in load_global(self)
   1088         module = self.readline()[:-1]
   1089         name = self.readline()[:-1]
-> 1090         klass = self.find_class(module, name)
   1091         self.append(klass)
   1092     dispatch[GLOBAL] = load_global

C:UsersTomAppDataLocalEnthoughtCanopyAppappdatacanopy-1.6.2.3262.win-x86_64libpickle.pyc in find_class(self, module, name)
   1122     def find_class(self, module, name):
   1123         # Subclasses may override this
-> 1124         __import__(module)
   1125         mod = sys.modules[module]
   1126         klass = getattr(mod, name)

ImportError: No module named copy_reg

I know that there is a difference between Python 3 and 2, in that file instead of open should be used in the dump (and I presume the pickle load) for Python 2, so I have tried both combinations in the code.

I am unsure what the error is telling me, so I haven't been able to get any further with this, any help on understanding the errors or fixing the problem appreciated.

Answer 1

The error with copy_reg was being caused by the write format in the code to pickle the figure, the correct code should include wb rather than w in the write statement as in:

# Save figure handle to disk
import pickle
with open('sinus.pickle', 'wb') as f: # should be 'wb' rather than 'w'
    pickle.dump(fig_handle, f) 

This was identified based on the copy_reg error and the solution provided in another question ImportError: No module named copy_reg pickle about copy_reg error when pickling.