cairo backend: default to pycairo

lazka · lazka · commit 23a43258390a · 2018-12-31T19:22:29.000+01:00
As seen in matplotlib#13042 it's a bit faster than cairocffi and it also takes 50 ms less time to import here. Also the GTK3Cairo backend requires pycairo, so there is a good chance it's already loaded anyway for that case.
diff --git a/.flake8 b/.flake8
@@ -32,7 +32,7 @@ per-file-ignores =
     matplotlib/_mathtext_data.py: E203, E261
     matplotlib/backends/_backend_tk.py: E501
     matplotlib/backends/backend_agg.py: E302
-    matplotlib/backends/backend_cairo.py: E203, E221, E402
+    matplotlib/backends/backend_cairo.py: E203, E221
     matplotlib/backends/backend_gtk3.py: E203, E221, E222, E225, E251, E501
     matplotlib/backends/backend_pgf.py: E731
     matplotlib/backends/qt_editor/_formlayout.py: E501
diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
@@ -11,24 +11,6 @@
 
 import numpy as np
 
-# cairocffi is more widely compatible than pycairo so try it first.
-try:
-    import cairocffi as cairo
-except ImportError:
-    try:
-        import cairo
-    except ImportError:
-        raise ImportError("cairo backend requires that cairocffi or pycairo "
-                          "is installed")
-    else:
-        if cairo.version_info < (1, 11, 0):
-            # Introduced create_for_data for Py3.
-            raise ImportError(
-                "cairo {} is installed; cairo>=1.11.0 is required"
-                .format(cairo.version))
-
-backend_version = cairo.version
-
 from .. import cbook
 from matplotlib.backend_bases import (
     _Backend, FigureCanvasBase, FigureManagerBase, GraphicsContextBase,
@@ -39,6 +21,27 @@
 from matplotlib.transforms import Affine2D
 
 
+def import_cairo():
+    try:
+        import cairo
+        if cairo.version_info < (1, 11, 0):
+            # Introduced create_for_data for Py3.
+            raise ImportError
+    except ImportError:
+        try:
+            import cairocffi as cairo
+        except ImportError:
+            raise ImportError(
+                "cairo backend requires that pycairo>=1.11.0 or cairocffi"
+                "is installed")
+
+    return cairo
+
+
+cairo = import_cairo()
+backend_version = cairo.version
+
+
 if cairo.__name__ == "cairocffi":
     # Convert a pycairo context to a cairocffi one.
     def _to_context(ctx):
