Preserve matplotlib axis line colors when converting from matplotlib

plotly/matplotlylib/renderer.py

@@ -11,6 +11,7 @@
 
 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
 
 
@@ -24,7 +25,10 @@ def _export_color(color):
     """
     if isinstance(color, str):
         return "rgba(0,0,0,0)" if color == "none" else color
-    return [_export_color(c) for c in color]
+    if isinstance(color, (list, tuple)) and all(isinstance(c, str) for c in color):
+        return [_export_color(c) for c in color]
+    bgcolor = export_color(color)
+    return "rgba(0,0,0,0)" if bgcolor == "none" else bgcolor
 
 
 class PlotlyRenderer(Renderer):
@@ -168,10 +172,16 @@ 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

@@ -199,3 +199,25 @@ def test_filled_path_collection_date_xaxis():
     filled = [t for t in plotly_fig.data if t.fill == "toself"]
     assert len(filled) >= 1
     assert all(isinstance(x, str) for x in filled[0].x)
+
+
+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"