Pull request #289: add backend

Merge in LCL/wolframclientforpython from feature/matplotlib to master

* commit 'be25946cfec47e308803a69794b3f6102a6c49f2':
  move backend location
  add backend

Author: crazyeng

wolframclient/language/hooks/__init__.py

@@ -0,0 +1,38 @@
+"""
+Custom matplotlib backend that sends figure image bytes to Wolfram via wl_print.
+
+Usage:
+    import matplotlib
+    matplotlib.use('module://backend_hello')
+    import matplotlib.pyplot as plt
+
+    plt.plot([1, 2, 3], [4, 5, 6])
+    plt.show()
+"""
+
+import io
+from matplotlib.backend_bases import FigureCanvasBase, FigureManagerBase
+from matplotlib.backends.backend_agg import FigureCanvasAgg
+from matplotlib._pylab_helpers import Gcf
+from wolframclient.language.side_effects import wl_print
+from wolframclient.language import wl, wlexpr
+
+
+class FigureCanvas(FigureCanvasAgg):
+    manager_class = type(None)  # placeholder, overridden below
+
+
+class FigureManager(FigureManagerBase):
+
+    @classmethod
+    def pyplot_show(cls, *, block=None):
+        for manager in Gcf.get_all_fig_managers():
+            manager.show()
+
+    def show(self):
+        buf = io.BytesIO()
+        self.canvas.figure.savefig(buf, format="png")
+        wl_print(wl.ImportByteArray(buf.getvalue(), "PNG"))
+
+
+FigureCanvas.manager_class = FigureManager