Make sure only one cairo binding is ever used; fix docs.

anntzer · anntzer · commit 017aeedc84d2 · 2017-06-20T12:26:59.000-07:00
diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
@@ -19,26 +19,30 @@
 
 import numpy as np
 
-try:
-    import cairocffi as cairo
-except ImportError:
+# In order to make it possible to pick the binding, use whichever has already
+# been imported, if any.  (The intermediate call to iter is just to placate
+# Python2.)
+cairo = next(
+    (mod for mod in (
+        sys.modules.get(name) for name in ["cairocffi", "cairo"]) if mod),
+    None)
+if cairo is None:
     try:
-        import cairo
+        import cairocffi as cairo
     except ImportError:
-        raise ImportError("Cairo backend requires that cairocffi or pycairo "
-                          "is installed.")
-    else:
-        HAS_CAIRO_CFFI = False
-else:
-    HAS_CAIRO_CFFI = True
-
-_version_required = (1, 2, 0)
-if cairo.version_info < _version_required:
-    raise ImportError("Pycairo %d.%d.%d is installed\n"
-                      "Pycairo %d.%d.%d or later is required"
-                      % (cairo.version_info + _version_required))
+        try:
+            import cairo
+        except ImportError:
+            raise ImportError(
+                "The cairo backend requires cairocffi or pycairo")
+# cairocffi can install itself as cairo (`install_as_pycairo`) -- don't get
+# fooled!
+HAS_CAIRO_CFFI = cairo.__name__ == "cairocffi"
+
+if cairo.version_info < (1, 2, 0):
+    raise ImportError("cairo {} is installed; "
+                      "cairo>=1.2.0 is required".format(cairo.version))
 backend_version = cairo.version
-del _version_required
 
 from matplotlib.backend_bases import (
     _Backend, FigureCanvasBase, FigureManagerBase, GraphicsContextBase,
diff --git a/lib/matplotlib/backends/backend_qt5cairo.py b/lib/matplotlib/backends/backend_qt5cairo.py
@@ -1,6 +1,5 @@
-import cairocffi as cairo
-
-from .backend_cairo import RendererCairo
+# Reimport cairo from backend_cairo, so that we use the same binding.
+from .backend_cairo import cairo, RendererCairo
 from .backend_qt5 import QtCore, QtGui, _BackendQT5, FigureCanvasQT
 from .qt_compat import QT_API
 
diff --git a/tutorials/01_introductory/usage.py b/tutorials/01_introductory/usage.py
@@ -430,7 +430,7 @@ def my_plotter(ax, data1, data2, param_dict):
 #           ``PySide``)
 # Qt5Agg    Agg rendering in a :term:`Qt5` canvas (requires PyQt5_)
 # Qt5Cairo  Cairo rendering in a :term:`Qt5` canvas (requires PyQt5_ and
-#           cairocffi_)
+#           pycairo_ or cairocffi_)
 # WxAgg     Agg rendering to to a :term:`wxWidgets` canvas (requires wxPython_)
 # macosx    Cocoa rendering in OSX windows
 #           (presently lacks blocking show() behavior when matplotlib is in
