Issue 1:
import matplotlib.pyplot as plt is erroring for matplotlib-1.5.3 while trying to import from PyQt4.

I have observed this while running on Travis-CI, linux, installing matplotlib using conda. Here is a trace-back from the python 3.4.2 failure (https://travis-ci.org/simpeg/simpeg/jobs/160737799), for 2.7.9, there is an example in the travis log: https://travis-ci.org/simpeg/simpeg/jobs/160737812)

import matplotlib.pyplot as plt
File "/home/travis/miniconda/lib/python3.4/site-packages/matplotlib/pyplot.py", line 114, in <module>
_backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
File "/home/travis/miniconda/lib/python3.4/site-packages/matplotlib/backends/__init__.py", line 32, in pylab_setup
globals(),locals(),[backend_name],0)
File "/home/travis/miniconda/lib/python3.4/site-packages/matplotlib/backends/backend_qt4agg.py", line 18, in <module>
from .backend_qt5agg import FigureCanvasQTAggBase as _FigureCanvasQTAggBase
File "/home/travis/miniconda/lib/python3.4/site-packages/matplotlib/backends/backend_qt5agg.py", line 16, in <module>
from .backend_qt5 import QtCore
File "/home/travis/miniconda/lib/python3.4/site-packages/matplotlib/backends/backend_qt5.py", line 31, in <module>
from .qt_compat import QtCore, QtGui, QtWidgets, _getSaveFileName, __version__
File "/home/travis/miniconda/lib/python3.4/site-packages/matplotlib/backends/qt_compat.py", line 137, in <module>
from PyQt4 import QtCore, QtGui
ImportError: No module named 'PyQt4'

The environment is

package | build
---------------------------|-----------------
expat-2.1.0 | 0 365 KB
icu-54.1 | 0 11.3 MB
jpeg-8d | 1 806 KB
libffi-3.2.1 | 0 36 KB
libgcc-5.2.0 | 0 1.1 MB
libgfortran-3.0.0 | 1 281 KB
libxcb-1.12 | 0 1.5 MB
mkl-11.3.3 | 0 122.1 MB
dbus-1.10.10 | 0 2.4 MB
glib-2.43.0 | 1 5.4 MB
libpng-1.6.22 | 0 214 KB
libxml2-2.9.2 | 0 4.2 MB
alabaster-0.7.9 | py34_0 11 KB
cython-0.24.1 | py34_0 6.3 MB
decorator-4.0.10 | py34_0 12 KB
docutils-0.12 | py34_2 673 KB
freetype-2.5.5 | 1 2.5 MB
gstreamer-1.8.0 | 0 2.6 MB
imagesize-0.7.1 | py34_0 3 KB
ipython_genutils-0.1.0 | py34_0 33 KB
markupsafe-0.23 | py34_2 32 KB
mpmath-0.19 | py34_1 901 KB
nose-1.3.7 | py34_1 196 KB
numpy-1.11.1 | py34_0 6.1 MB
path.py-8.2.1 | py34_0 47 KB
ptyprocess-0.5.1 | py34_0 19 KB
pygments-2.1.3 | py34_0 1.2 MB
pyparsing-2.1.4 | py34_0 72 KB
pytz-2016.6.1 | py34_0 177 KB
pyyaml-3.12 | py34_0 348 KB
setuptools-27.2.0 | py34_0 528 KB
simplegeneric-0.8.1 | py34_1 7 KB
sip-4.18 | py34_0 240 KB
six-1.10.0 | py34_0 17 KB
snowballstemmer-1.2.1 | py34_0 79 KB
sphinx_rtd_theme-0.1.9 | py34_0 628 KB
wcwidth-0.1.7 | py34_0 21 KB
wheel-0.29.0 | py34_0 82 KB
babel-2.3.4 | py34_0 4.8 MB
cycler-0.10.0 | py34_0 11 KB
fontconfig-2.11.1 | 6 405 KB
gst-plugins-base-1.8.0 | 0 3.1 MB
jinja2-2.8 | py34_1 304 KB
pexpect-4.0.1 | py34_0 66 KB
pickleshare-0.7.4 | py34_0 9 KB
pip-8.1.2 | py34_0 1.6 MB
prompt_toolkit-1.0.3 | py34_0 309 KB
python-dateutil-2.5.3 | py34_0 238 KB
scipy-0.18.0 | np111py34_0 30.7 MB
sympy-1.0 | py34_0 5.9 MB
traitlets-4.3.0 | py34_0 125 KB
ipython-5.1.0 | py34_0 994 KB
qt-5.6.0 | 0 43.9 MB
sphinx-1.4.1 | py34_0 1.3 MB
pyqt-5.6.0 | py34_0 5.2 MB
matplotlib-1.5.3 | np111py34_0 8.4 MB
------------------------------------------------------------
Total: 279.6 MB

This was not an issue when using matplotlib-1.5.1 and pyqt-4.11.4 (https://travis-ci.org/simpeg/simpeg/jobs/159897876#L379)

Thanks for your help!

Issue 2:
Our pandas tests on travis started to fail last night on python 3.5 (eg https://travis-ci.org/pydata/pandas/jobs/160584906) with errors in our plotting tests (among others: "ImportError: No module named 'PyQt4'").

Compared to the previous build that passed, I noticed the difference in matplotlib and pyqt versions (matplotlib 1.5.1 -> 1.5.3, pyqt-4.11.4 -> pyqt-5.6.0, qt-4.8.7 -> qt-5.6.0). I could also reproduce this locally with conda create -n test-mpl python=3.5 matplotlib -c defaults, then importing matplotlib.pyplot gives the above error.

I am not sure if this has anything to do with matplotlib itself, or rather a broken build in anaconda, but reporting it here to be sure.