Preserve matplotlib axis line colors when converting from matplotlib

plotly/matplotlylib/renderer.py

@@ -11,9 +11,20 @@
 
 import plotly.graph_objs as go
 from plotly.matplotlylib.mplexporter import Renderer
+from plotly.matplotlylib.mplexporter.utils import export_color
 from plotly.matplotlylib import mpltools
 
 
+def _export_color(color):
+    """Export a matplotlib color for use as a plotly color.
+
+    matplotlib uses "none" for fully transparent colors, which plotly does not
+    accept, so transparent colors are exported as transparent black.
+    """
+    color = export_color(color)
+    return "rgba(0,0,0,0)" if color == "none" else color
+
+
 class PlotlyRenderer(Renderer):
     """A renderer class inheriting from base for rendering mpl plots in plotly.
 
@@ -146,10 +157,16 @@ def open_axes(self, ax, props):
         self.axis_ct += 1
         # set defaults in axes
         xaxis = go.layout.XAxis(
-            anchor="y{0}".format(self.axis_ct), zeroline=False, ticks="inside"
+            anchor="y{0}".format(self.axis_ct),
+            zeroline=False,
+            ticks="inside",
+            linecolor=_export_color(ax.spines["bottom"].get_edgecolor()),
         )
         yaxis = go.layout.YAxis(
-            anchor="x{0}".format(self.axis_ct), zeroline=False, ticks="inside"
+            anchor="x{0}".format(self.axis_ct),
+            zeroline=False,
+            ticks="inside",
+            linecolor=_export_color(ax.spines["left"].get_edgecolor()),
         )
         # update defaults with things set in mpl
         mpl_xaxis, mpl_yaxis = mpltools.prep_xy_axis(

plotly/matplotlylib/tests/test_renderer.py

@@ -84,3 +84,26 @@ def test_multiple_traces_native_legend():
     assert plotly_fig.data[0].mode == "lines"
     assert plotly_fig.data[1].mode == "markers"
     assert plotly_fig.data[2].mode == "lines+markers"
+
+
+
+def test_axis_linecolor_defaults_to_black():
+    fig, ax = plt.subplots()
+    ax.plot([0, 1], [0, 1])
+
+    plotly_fig = tls.mpl_to_plotly(fig)
+
+    assert plotly_fig.layout.xaxis.linecolor == "#000000"
+    assert plotly_fig.layout.yaxis.linecolor == "#000000"
+
+
+def test_custom_axis_linecolors_are_preserved():
+    fig, ax = plt.subplots()
+    ax.spines["bottom"].set_color("red")
+    ax.spines["left"].set_color("green")
+    ax.plot([0, 1], [0, 1])
+
+    plotly_fig = tls.mpl_to_plotly(fig)
+
+    assert plotly_fig.layout.xaxis.linecolor == "#FF0000"
+    assert plotly_fig.layout.yaxis.linecolor == "#008000"