MNT: make error message more verbose

Author: tacaswell

lib/matplotlib/backends/qt_compat.py

@@ -141,7 +141,9 @@ def _getSaveFileName(*args, **kwargs):
                 return QtGui.QFileDialog.getSaveFileName(*args, **kwargs), None
 
     else:
-        raise RuntimeError("No PyQt bindings found despite sip importing")
+        raise RuntimeError("PyQt{4,5} bindings found despite sip importing\n"
+                           "Please install PyQt4 or PyQt5, uninstall sip or "
+                           "explicitly set the pyside backend.")
 
     # Alias PyQt-specific functions for PySide compatibility.
     QtCore.Signal = QtCore.pyqtSignal