PX shouldn't modify attrs controlled by template

packages/python/plotly/plotly/express/_core.py

@@ -375,16 +375,18 @@ def configure_cartesian_marginal_axes(args, fig, orders):
 
     # Configure axis ticks on marginal subplots
     if args["marginal_x"]:
-        fig.update_yaxes(
-            showticklabels=False, showgrid=args["marginal_x"] == "histogram", row=nrows
-        )
-        fig.update_xaxes(showgrid=True, row=nrows)
+        fig.update_yaxes(showticklabels=False, row=nrows)
+        if args["template"].layout.yaxis.showgrid is None:
+            fig.update_yaxes(showgrid=args["marginal_x"] == "histogram", row=nrows)
+        if args["template"].layout.xaxis.showgrid is None:
+            fig.update_xaxes(showgrid=True, row=nrows)
 
     if args["marginal_y"]:
-        fig.update_xaxes(
-            showticklabels=False, showgrid=args["marginal_y"] == "histogram", col=ncols
-        )
-        fig.update_yaxes(showgrid=True, col=ncols)
+        fig.update_xaxes(showticklabels=False, col=ncols)
+        if args["template"].layout.xaxis.showgrid is None:
+            fig.update_xaxes(showgrid=args["marginal_y"] == "histogram", col=ncols)
+        if args["template"].layout.yaxis.showgrid is None:
+            fig.update_yaxes(showgrid=True, col=ncols)
 
     # Add axis titles to non-marginal subplots
     y_title = get_decorated_label(args, args["y"], "y")
@@ -687,55 +689,47 @@ def apply_default_cascade(args):
         else:
             args["template"] = "plotly"
 
-    # retrieve the actual template if we were given a name
     try:
-        template = pio.templates[args["template"]]
+        # retrieve the actual template if we were given a name
+        args["template"] = pio.templates[args["template"]]
     except Exception:
-        template = args["template"]
+        # otherwise try to build a real template
+        args["template"] = go.layout.Template(args["template"])
 
     # if colors not set explicitly or in px.defaults, defer to a template
     # if the template doesn't have one, we set some final fallback defaults
     if "color_continuous_scale" in args:
-        if args["color_continuous_scale"] is None:
-            try:
-                args["color_continuous_scale"] = [
-                    x[1] for x in template.layout.colorscale.sequential
-                ]
-            except (AttributeError, TypeError):
-                pass
+        if (
+            args["color_continuous_scale"] is None
+            and args["template"].layout.colorscale.sequential
+        ):
+            args["color_continuous_scale"] = [
+                x[1] for x in args["template"].layout.colorscale.sequential
+            ]
         if args["color_continuous_scale"] is None:
             args["color_continuous_scale"] = sequential.Viridis
 
     if "color_discrete_sequence" in args:
-        if args["color_discrete_sequence"] is None:
-            try:
-                args["color_discrete_sequence"] = template.layout.colorway
-            except (AttributeError, TypeError):
-                pass
+        if args["color_discrete_sequence"] is None and args["template"].layout.colorway:
+            args["color_discrete_sequence"] = args["template"].layout.colorway
         if args["color_discrete_sequence"] is None:
             args["color_discrete_sequence"] = qualitative.D3
 
     # if symbol_sequence/line_dash_sequence not set explicitly or in px.defaults,
     # see if we can defer to template. If not, set reasonable defaults
     if "symbol_sequence" in args:
-        if args["symbol_sequence"] is None:
-            try:
-                args["symbol_sequence"] = [
-                    scatter.marker.symbol for scatter in template.data.scatter
-                ]
-            except (AttributeError, TypeError):
-                pass
+        if args["symbol_sequence"] is None and args["template"].data.scatter:
+            args["symbol_sequence"] = [
+                scatter.marker.symbol for scatter in args["template"].data.scatter
+            ]
         if not args["symbol_sequence"] or not any(args["symbol_sequence"]):
             args["symbol_sequence"] = ["circle", "diamond", "square", "x", "cross"]
 
     if "line_dash_sequence" in args:
-        if args["line_dash_sequence"] is None:
-            try:
-                args["line_dash_sequence"] = [
-                    scatter.line.dash for scatter in template.data.scatter
-                ]
-            except (AttributeError, TypeError):
-                pass
+        if args["line_dash_sequence"] is None and args["template"].data.scatter:
+            args["line_dash_sequence"] = [
+                scatter.line.dash for scatter in args["template"].data.scatter
+            ]
         if not args["line_dash_sequence"] or not any(args["line_dash_sequence"]):
             args["line_dash_sequence"] = [
                 "solid",
@@ -1264,13 +1258,17 @@ def make_figure(args, constructor, trace_patch={}, layout_patch={}):
             cmax=range_color[1],
             colorbar=dict(title=get_decorated_label(args, args[colorvar], colorvar)),
         )
-    for v in ["title", "height", "width", "template"]:
+    for v in ["title", "height", "width"]:
         if args[v]:
             layout_patch[v] = args[v]
     layout_patch["legend"] = {"tracegroupgap": 0}
-    if "title" not in layout_patch:
+    if "title" not in layout_patch and args["template"].layout.margin.t is None:
         layout_patch["margin"] = {"t": 60}
-    if "size" in args and args["size"]:
+    if (
+        "size" in args
+        and args["size"]
+        and args["template"].layout.legend.itemsizing is None
+    ):
         layout_patch["legend"]["itemsizing"] = "constant"
 
     fig = init_figure(
@@ -1295,6 +1293,8 @@ def make_figure(args, constructor, trace_patch={}, layout_patch={}):
     # Add traces, layout and frames to figure
     fig.add_traces(frame_list[0]["data"] if len(frame_list) > 0 else [])
     fig.layout.update(layout_patch)
+    if "template" in args and args["template"] is not None:
+        fig.update_layout(template=args["template"], overwrite=True)
     fig.frames = frame_list if len(frames) > 1 else []
 
     fig._px_trendlines = pd.DataFrame(trendline_rows)

packages/python/plotly/plotly/tests/test_core/test_px/test_px.py

@@ -51,3 +51,110 @@ def test_custom_data_scatter():
         fig.data[0].hovertemplate
         == "sepal_width=%{x}<br>sepal_length=%{y}<br>petal_length=%{customdata[2]}<br>petal_width=%{customdata[3]}<br>species_id=%{customdata[0]}"
     )
+
+
+def test_px_templates():
+    import plotly.io as pio
+    import plotly.graph_objects as go
+
+    tips = px.data.tips()
+
+    # use the normal defaults
+    fig = px.scatter()
+    assert fig.layout.template == pio.templates[pio.templates.default]
+
+    # respect changes to defaults
+    pio.templates.default = "seaborn"
+    fig = px.scatter()
+    assert fig.layout.template == pio.templates["seaborn"]
+
+    # special px-level defaults over pio defaults
+    pio.templates.default = "seaborn"
+    px.defaults.template = "ggplot2"
+    fig = px.scatter()
+    assert fig.layout.template == pio.templates["ggplot2"]
+
+    # accept names in args over pio and px defaults
+    fig = px.scatter(template="seaborn")
+    assert fig.layout.template == pio.templates["seaborn"]
+
+    # accept objects in args
+    fig = px.scatter(template={})
+    assert fig.layout.template == go.layout.Template()
+
+    # read colorway from the template
+    fig = px.scatter(
+        tips,
+        x="total_bill",
+        y="tip",
+        color="sex",
+        template=dict(layout_colorway=["red", "blue"]),
+    )
+    assert fig.data[0].marker.color == "red"
+    assert fig.data[1].marker.color == "blue"
+
+    # default colorway fallback
+    fig = px.scatter(tips, x="total_bill", y="tip", color="sex", template=dict())
+    assert fig.data[0].marker.color == px.colors.qualitative.D3[0]
+    assert fig.data[1].marker.color == px.colors.qualitative.D3[1]
+
+    # pio default template colorway fallback
+    pio.templates.default = "seaborn"
+    px.defaults.template = None
+    fig = px.scatter(tips, x="total_bill", y="tip", color="sex")
+    assert fig.data[0].marker.color == pio.templates["seaborn"].layout.colorway[0]
+    assert fig.data[1].marker.color == pio.templates["seaborn"].layout.colorway[1]
+
+    # pio default template colorway fallback
+    pio.templates.default = "seaborn"
+    px.defaults.template = "ggplot2"
+    fig = px.scatter(tips, x="total_bill", y="tip", color="sex")
+    assert fig.data[0].marker.color == pio.templates["ggplot2"].layout.colorway[0]
+    assert fig.data[1].marker.color == pio.templates["ggplot2"].layout.colorway[1]
+
+    # don't overwrite top margin when set in template
+    fig = px.scatter(title="yo")
+    assert fig.layout.margin.t is None
+
+    fig = px.scatter()
+    assert fig.layout.margin.t == 60
+
+    fig = px.scatter(template=dict(layout_margin_t=2))
+    assert fig.layout.margin.t is None
+
+    # don't force histogram gridlines when set in template
+    pio.templates.default = "none"
+    px.defaults.template = None
+    fig = px.scatter(
+        tips, x="total_bill", y="tip", marginal_x="histogram", marginal_y="histogram"
+    )
+    assert fig.layout.xaxis2.showgrid
+    assert fig.layout.xaxis3.showgrid
+    assert fig.layout.yaxis2.showgrid
+    assert fig.layout.yaxis3.showgrid
+
+    fig = px.scatter(
+        tips,
+        x="total_bill",
+        y="tip",
+        marginal_x="histogram",
+        marginal_y="histogram",
+        template=dict(layout_yaxis_showgrid=False),
+    )
+    assert fig.layout.xaxis2.showgrid
+    assert fig.layout.xaxis3.showgrid
+    assert fig.layout.yaxis2.showgrid is None
+    assert fig.layout.yaxis3.showgrid is None
+
+    fig = px.scatter(
+        tips,
+        x="total_bill",
+        y="tip",
+        marginal_x="histogram",
+        marginal_y="histogram",
+        template=dict(layout_xaxis_showgrid=False),
+    )
+    assert fig.layout.xaxis2.showgrid is None
+    assert fig.layout.xaxis3.showgrid is None
+    assert fig.layout.yaxis2.showgrid
+    assert fig.layout.yaxis3.showgrid