Add consistent legend support across backends

src/arviz_plots/backend/bokeh/legend.py

@@ -19,7 +19,8 @@ def legend(
     artist_type="line",
     artist_kwargs=None,
     legend_target=None,
-    side="right",
+    side="auto",
+    legend_placement_threshold=600,  # Magic number
     **kwargs,
 ):
     """Generate a legend on a figure given lists of labels and property kwargs.
@@ -61,6 +62,14 @@ def legend(
     for kws in kwarg_list:
         glyph = artist_fun(**{**artist_kwargs, **kws})
         glyph_list.append(glyph)
+
+    if side == "auto":
+        plot_width = target_plot.width
+        if plot_width >= legend_placement_threshold:
+            side = "right"
+        else:
+            side = "center"
+
     leg = Legend(
         items=[(str(label), [glyph]) for label, glyph in zip(label_list, glyph_list)],
         title=title,

src/arviz_plots/backend/none/__init__.py

@@ -11,6 +11,8 @@
 
 import numpy as np
 
+from .legend import legend
+
 ALLOW_KWARGS = True
 
 
@@ -532,16 +534,3 @@ def grid(target, axis, color):
     }
     target.append(artist_element)
     return artist_element
-
-
-def legend(
-    target,
-    kwarg_list,
-    label_list,
-    title=None,  # pylint: disable=redefined-outer-name
-    artist_type="line",
-    artist_kwargs=None,
-    **kwargs,
-):
-    """Interface to manually generated legends."""
-    raise NotImplementedError("No legends in 'none' backend.")

src/arviz_plots/backend/none/legend.py

@@ -0,0 +1,25 @@
+"""None backend manual legend generation.
+
+For now only used for documentation purposes.
+"""
+
+
+# pylint: disable=unused-argument
+def legend(
+    target, kwarg_list, label_list, title=None, artist_type="line", artist_kwargs=None, **kwargs
+):
+    """Generate a legend on a figure given lists of labels and property kwargs.
+
+    Parameters
+    ----------
+    target : plot object
+    kwarg_list : sequence of mapping
+    label_list : sequence of str
+    title : str, optional
+    artist_type : {"line", "scatter", "rectangle"}, default "line"
+    artist_kwargs : mapping, optional
+        Passed to all artists when generating legend miniatures.
+    **kwargs
+        Passed to backend legend generating function.
+    """
+    return None

src/arviz_plots/backend/plotly/__init__.py

@@ -16,6 +16,7 @@
 from webcolors import hex_to_rgb, name_to_rgb
 
 from ..none import get_default_aes as get_agnostic_default_aes
+from .legend import legend
 
 
 class UnsetDefault:

src/arviz_plots/backend/plotly/legend.py

@@ -1,8 +1,58 @@
 """Plotly legend generation."""
 
 
+def dealiase_line_kwargs(kwargs):
+    """Convert arviz common interface properties to plotly ones."""
+    prop_map = {"linewidth": "width", "linestyle": "dash"}
+    return {prop_map.get(key, key): value for key, value in kwargs.items()}
+
+
 def legend(
     target, kwarg_list, label_list, title=None, artist_type="line", artist_kwargs=None, **kwargs
 ):
-    """Generate a legend with plotly."""
-    raise NotImplementedError("Still in progress")
+    """Generate a legend with plotly.
+
+    Parameters
+    ----------
+    target : plotly.graph_objects.Figure
+        The figure to add the legend to
+    kwarg_list : list
+        List of style dictionaries for each legend entry
+    label_list : list
+        List of labels for each legend entry
+    title : str, optional
+        Title of the legend
+    artist_type : str, optional
+        Type of artist to use for legend entries. Currently only "line" is supported.
+    artist_kwargs : dict, optional
+        Additional kwargs passed to all artists
+    **kwargs : dict
+        Additional kwargs passed to legend configuration
+
+    Returns
+    -------
+    None
+        The legend is added to the target figure inplace
+    """
+    if artist_kwargs is None:
+        artist_kwargs = {}
+
+    if artist_type == "line":
+        artist_fun = target.add_scatter
+        kwarg_list = [dealiase_line_kwargs(kws) for kws in kwarg_list]
+        mode = "lines"
+    else:
+        raise NotImplementedError("Only line type legends supported for now")
+
+    for kws, label in zip(kwarg_list, label_list):
+        artist_fun(
+            x=[None],
+            y=[None],
+            name=str(label),
+            mode=mode,
+            line=kws,
+            showlegend=True,
+            **artist_kwargs,
+        )
+
+    target.update_layout(showlegend=True, legend_title_text=title, **kwargs)

src/arviz_plots/plots/psense_dist_plot.py

@@ -274,4 +274,10 @@ def plot_psense_dist(
         stats_kwargs=stats_kwargs,
     )
 
+    # Add legend for alpha parameter automatically
+    plot_collection.add_legend(
+        "alpha",
+        title="Power Scale Factor",
+    )
+
     return plot_collection