To help us understand and resolve your issue please check that you have provided
the information below.

• Matplotlib version, Python version and Platform (Windows, OSX, Linux ...)

1.5.1, 2.7.11/3.5.1, Fedora rawhide

• How did you install Matplotlib and Python (pip, anaconda, from source ...)

From Fedora package.

• If possible please supply a Short, Self Contained, Correct, Example
  that demonstrates the issue i.e a small piece of code which reproduces the issue
  and can be run with out any other (or as few as possible) external dependencies.

Try building Pympler (http://pythonhosted.org/Pympler/) and running its tests (python3 setup.py test). On armv7hl, I get this exception:

Traceback (most recent call last):
  File "/builddir/build/BUILD/Pympler-0.4.3/test/tracker/test_classtracker.py", line 178, in test_snapshot_members
    self.tracker.create_snapshot(compute_total=True)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/classtracker.py", line 567, in create_snapshot
    snapshot.asizeof_total = asizeof.asizeof(all=True, code=True)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 2191, in asizeof
    s = _asizer.asizeof(*t)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 1783, in asizeof
    s, _ = self._sizes(objs, None)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 1753, in _sizes
    s[i] = self._sizer(o, 0, sized)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 1729, in _sizer
    s += z(o, d, None)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 1729, in _sizer
    s += z(o, d, None)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 1729, in _sizer
    s += z(o, d, None)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 1729, in _sizer
    s += z(o, d, None)
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 1728, in _sizer
    for o in r(obj, False):
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 536, in _refs
    for _, o in _dir2(obj, **kwds):
  File "/builddir/build/BUILDROOT/python-Pympler-0.4.3-1.fc25.noarch/usr/lib/python3.5/site-packages/pympler/asizeof.py", line 347, in _dir2
    if hasattr(obj, slots):
  File "/usr/lib/python3.5/site-packages/matplotlib/externals/six.py", line 116, in __getattr__
    _module = self._resolve()
  File "/usr/lib/python3.5/site-packages/matplotlib/externals/six.py", line 113, in _resolve
    return _import_module(self.mod)
  File "/usr/lib/python3.5/site-packages/matplotlib/externals/six.py", line 80, in _import_module
    __import__(name)
ImportError: No module named 'winreg'

The bundled six.py has this:

class _MovedItems(_LazyModule):
    """Lazy loading of moved objects"""
    __path__ = []  # mark as package


_moved_attributes = [
...
    MovedModule("winreg", "_winreg"),
]

while python-six-1.10.0 (latest version) has this:

# Add windows specific modules.
if sys.platform == "win32":
    _moved_attributes += [
        MovedModule("winreg", "_winreg"),
    ]

I applied this patch:

diff -up matplotlib-1.5.1/setupext.py.six matplotlib-1.5.1/setupext.py
--- matplotlib-1.5.1/setupext.py.six    2016-01-10 23:20:20.000000000 +0100
+++ matplotlib-1.5.1/setupext.py    2016-05-18 13:44:21.534494158 +0200
@@ -1026,6 +1026,18 @@ class Qhull(SetupPackage):
             ext.sources.extend(glob.glob('extern/qhull/*.c'))


+class Six(SetupPackage):
+    name = "six"
+
+    def check(self):
+        try:
+            import six
+        except ImportError:
+            return 'not found. pip may install it below.'
+
+        return 'version %s' % six.__version__
+
+
 class TTConv(SetupPackage):
     name = "ttconv"

diff -up matplotlib-1.5.1/setup.py.six matplotlib-1.5.1/setup.py
--- matplotlib-1.5.1/setup.py.six   2016-01-10 23:20:20.000000000 +0100
+++ matplotlib-1.5.1/setup.py   2016-05-18 13:44:21.528494040 +0200
@@ -84,7 +84,7 @@ mpl_packages = [
     setupext.Delaunay(),
     setupext.QhullWrap(),
     setupext.Tri(),
-    setupext.Externals(),
+    setupext.Six(),
     'Optional subpackages',
     setupext.SampleData(),
     setupext.Toolkits(),

and replaced all imports from bundled six to system-wide six without any adverse effects. Please consider unbundling six and using system-wide version.