ImportError: cannot import name 'QtCore'

Question

I am getting the below error with the following imports. It seems to be related to pandas import. I am unsure how to debug/solve this.

Imports:

import pandas as pd
import numpy as np
import pdb, math, pickle
import matplotlib.pyplot as plt

Error:

In [1]: %run NN.py
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
/home/abhishek/Desktop/submission/a1/new/NN.py in <module>()
      2 import numpy as np
      3 import pdb, math, pickle
----> 4 import matplotlib.pyplot as plt
      5 
      6 class NN(object):

/home/abhishek/anaconda3/lib/python3.5/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

/home/abhishek/anaconda3/lib/python3.5/site-packages/matplotlib/backends/__init__.py 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

/home/abhishek/anaconda3/lib/python3.5/site-packages/matplotlib/backends/backend_qt4agg.py in <module>()
     16 
     17 
---> 18 from .backend_qt5agg import FigureCanvasQTAggBase as _FigureCanvasQTAggBase
     19 
     20 from .backend_agg import FigureCanvasAgg

/home/abhishek/anaconda3/lib/python3.5/site-packages/matplotlib/backends/backend_qt5agg.py in <module>()
     14 
     15 from .backend_agg import FigureCanvasAgg
---> 16 from .backend_qt5 import QtCore
     17 from .backend_qt5 import QtGui
     18 from .backend_qt5 import FigureManagerQT

/home/abhishek/anaconda3/lib/python3.5/site-packages/matplotlib/backends/backend_qt5.py in <module>()
     29     figureoptions = None
     30 
---> 31 from .qt_compat import QtCore, QtGui, QtWidgets, _getSaveFileName, __version__
     32 from matplotlib.backends.qt_editor.formsubplottool import UiSubplotTool
     33 

/home/abhishek/anaconda3/lib/python3.5/site-packages/matplotlib/backends/qt_compat.py in <module>()
    135     # have been changed in the above if block
    136     if QT_API in [QT_API_PYQT, QT_API_PYQTv2]:  # PyQt4 API
--> 137         from PyQt4 import QtCore, QtGui
    138 
    139         try:

ImportError: cannot import name 'QtCore'

Debugging:

$ python -c "import PyQt4"
$ python -c "from PyQt4 import QtCore"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: cannot import name 'QtCore'
$ conda list | grep qt
jupyter-qtconsole-colorschemes 0.7.1                     <pip>
pyqt                      5.6.0                    py35_0  
qt                        5.6.0                         0  
qtawesome                 0.3.3                    py35_0  
qtconsole                 4.2.1                    py35_0  
qtpy                      1.0.2                    py35_0 

I found other answers but all related to Windows. I am using ubuntu 16.04 with anaconda distribution of python 3.

Answer 1

Downgrading pyqt version 5.6.0 to 4.11.4, and qt from version 5.6.0 to 4.8.7 fixes this:

$ conda install pyqt=4.11.4
$ conda install qt=4.8.7

The issue itself is being resolved here: https://github.com/ContinuumIO/anaconda-issues/issues/1068

Answer 2

To avoid downgrading you can also (as was suggested by tacaswell in the issue) set the backend to use Qt5Agg using one of the methods here: http://matplotlib.org/faq/usage_faq.html#what-is-a-backend

E.g., you can modify the matplotlibrc file located in /your/path/to/anaconda3/envs/yourenv/lib/python3.5/site-packages/matplotlib/mpl-data/matplotlibrc and change the backend line to backend : Qt5Agg. This will make the Qt5Agg backend the default throughout the yourenv conda environment.

Answer 3

Updating matplotlib did the trick for me:

conda install matplotlib