Add Scale.label interface for formatting ticks (#2877)

* Step one of bikeshedding scale names

* Remove concept of separate Scale / ScaleSpec

* Begin transitioning Scale tick/label parameterization to declarations

* Add initial draft of Continuous.label API

* Note to self

* Add label tests

* Add docstring for Continuous.label

* Fix tests

* Partialy update Nominal

* Hide _priority from dataclass signature

* A little more test coverage and documentation

* MPL<3.3 compat in temporal tests

* Use (sym)log locator / formatter for symlog scales by default

* Remove code duplication

* Rename transform parameter to trans

* Pass through residual TODO comments

* Lint

seaborn/_core/plot.py

@@ -23,7 +23,7 @@
 from seaborn._stats.base import Stat
 from seaborn._core.data import PlotData
 from seaborn._core.moves import Move
-from seaborn._core.scales import ScaleSpec, Scale
+from seaborn._core.scales import Scale
 from seaborn._core.subplots import Subplots
 from seaborn._core.groupby import GroupBy
 from seaborn._core.properties import PROPERTIES, Property, Coordinate
@@ -146,7 +146,7 @@ class Plot:
 
     _data: PlotData
     _layers: list[Layer]
-    _scales: dict[str, ScaleSpec]
+    _scales: dict[str, Scale]
 
     _subplot_spec: dict[str, Any]  # TODO values type
     _facet_spec: FacetSpec
@@ -520,7 +520,7 @@ def facet(
 
     # TODO def twin()?
 
-    def scale(self, **scales: ScaleSpec) -> Plot:
+    def scale(self, **scales: Scale) -> Plot:
         """
         Control mappings from data units to visual properties.
 
@@ -873,7 +873,7 @@ def _transform_coords(self, p: Plot, common: PlotData, layers: list[Layer]) -> N
                 var_df = pd.DataFrame(columns=cols)
 
             prop = Coordinate(axis)
-            scale_spec = self._get_scale(p, prefix, prop, var_df[var])
+            scale = self._get_scale(p, prefix, prop, var_df[var])
 
             # Shared categorical axes are broken on matplotlib<3.4.0.
             # https://github.com/matplotlib/matplotlib/pull/18308
@@ -882,7 +882,7 @@ def _transform_coords(self, p: Plot, common: PlotData, layers: list[Layer]) -> N
             if Version(mpl.__version__) < Version("3.4.0"):
                 from seaborn._core.scales import Nominal
                 paired_axis = axis in p._pair_spec
-                cat_scale = isinstance(scale_spec, Nominal)
+                cat_scale = isinstance(scale, Nominal)
                 ok_dim = {"x": "col", "y": "row"}[axis]
                 shared_axes = share_state not in [False, "none", ok_dim]
                 if paired_axis and cat_scale and shared_axes:
@@ -897,7 +897,7 @@ def _transform_coords(self, p: Plot, common: PlotData, layers: list[Layer]) -> N
             # Setup the scale on all of the data and plug it into self._scales
             # We do this because by the time we do self._setup_scales, coordinate data
             # will have been converted to floats already, so scale inference fails
-            self._scales[var] = scale_spec.setup(var_df[var], prop)
+            self._scales[var] = scale._setup(var_df[var], prop)
 
             # Set up an empty series to receive the transformed values.
             # We need this to handle piecemeal tranforms of categories -> floats.
@@ -927,7 +927,7 @@ def _transform_coords(self, p: Plot, common: PlotData, layers: list[Layer]) -> N
 
                     seed_values = var_df.loc[idx, var]
 
-                scale = scale_spec.setup(seed_values, prop, axis=axis_obj)
+                scale = scale._setup(seed_values, prop, axis=axis_obj)
 
                 for layer, new_series in zip(layers, transformed_data):
                     layer_df = layer["data"].frame
@@ -936,7 +936,7 @@ def _transform_coords(self, p: Plot, common: PlotData, layers: list[Layer]) -> N
                         new_series.loc[idx] = scale(layer_df.loc[idx, var])
 
                 # TODO need decision about whether to do this or modify axis transform
-                set_scale_obj(view["ax"], axis, scale.matplotlib_scale)
+                set_scale_obj(view["ax"], axis, scale._matplotlib_scale)
 
             # Now the transformed data series are complete, set update the layer data
             for layer, new_series in zip(layers, transformed_data):
@@ -1000,11 +1000,11 @@ def _compute_stats(self, spec: Plot, layers: list[Layer]) -> None:
 
     def _get_scale(
         self, spec: Plot, var: str, prop: Property, values: Series
-    ) -> ScaleSpec:
+    ) -> Scale:
 
         if var in spec._scales:
             arg = spec._scales[var]
-            if arg is None or isinstance(arg, ScaleSpec):
+            if arg is None or isinstance(arg, Scale):
                 scale = arg
             else:
                 scale = prop.infer_scale(arg, values)
@@ -1052,28 +1052,28 @@ def _setup_scales(self, p: Plot, layers: list[Layer]) -> None:
                 axis = m["axis"]
 
             prop = PROPERTIES.get(var if axis is None else axis, Property())
-            scale_spec = self._get_scale(p, var, prop, var_values)
+            scale = self._get_scale(p, var, prop, var_values)
 
             # Initialize the data-dependent parameters of the scale
             # Note that this returns a copy and does not mutate the original
             # This dictionary is used by the semantic mappings
-            if scale_spec is None:
+            if scale is None:
                 # TODO what is the cleanest way to implement identity scale?
-                # We don't really need a ScaleSpec, and Identity() will be
+                # We don't really need a Scale, and Identity() will be
                 # overloaded anyway (but maybe a general Identity object
                 # that can be used as Scale/Mark/Stat/Move?)
                 # Note that this may not be the right spacer to use
                 # (but that is only relevant for coordinates, where identity scale
                 # doesn't make sense or is poorly defined, since we don't use pixels.)
-                self._scales[var] = Scale([], lambda x: x, None, "identity", None)
+                self._scales[var] = Scale._identity()
             else:
-                scale = scale_spec.setup(var_values, prop)
+                scale = scale._setup(var_values, prop)
                 if isinstance(prop, Coordinate):
                     # If we have a coordinate here, we didn't assign a scale for it
                     # in _transform_coords, which means it was added during compute_stat
                     # This allows downstream orientation inference to work properly.
                     # But it feels a little hacky, so perhaps revisit.
-                    scale.scale_type = "computed"
+                    scale._priority = 0  # type: ignore
                 self._scales[var] = scale
 
     def _plot_layer(self, p: Plot, layer: Layer) -> None:
@@ -1097,14 +1097,14 @@ def get_order(var):
                 # sorted unique numbers will correctly reconstruct intended order
                 # TODO This is tricky, make sure we add some tests for this
                 if var not in "xy" and var in scales:
-                    return scales[var].order
+                    return getattr(scales[var], "order", None)
 
             if "width" in mark._mappable_props:
                 width = mark._resolve(df, "width", None)
             else:
                 width = df.get("width", 0.8)  # TODO what default
             if orient in df:
-                df["width"] = width * scales[orient].spacing(df[orient])
+                df["width"] = width * scales[orient]._spacing(df[orient])
 
             if "baseline" in mark._mappable_props:
                 # TODO what marks should have this?
@@ -1277,7 +1277,7 @@ def _setup_split_generator(
             v for v in grouping_vars if v in df and v not in ["col", "row"]
         ]
         for var in grouping_vars:
-            order = self._scales[var].order
+            order = getattr(self._scales[var], "order", None)
             if order is None:
                 order = categorical_order(df[var])
             grouping_keys.append(order)
@@ -1357,7 +1357,7 @@ def _update_legend_contents(
         ]] = []
         schema = []
         for var in legend_vars:
-            var_legend = scales[var].legend
+            var_legend = scales[var]._legend
             if var_legend is not None:
                 values, labels = var_legend
                 for (_, part_id), part_vars, _ in schema:

seaborn/_core/properties.py

@@ -8,7 +8,7 @@
 from matplotlib.colors import to_rgb, to_rgba, to_rgba_array
 from matplotlib.path import Path
 
-from seaborn._core.scales import ScaleSpec, Nominal, Continuous, Temporal
+from seaborn._core.scales import Scale, Nominal, Continuous, Temporal
 from seaborn._core.rules import categorical_order, variable_type
 from seaborn._compat import MarkerStyle
 from seaborn.palettes import QUAL_PALETTES, color_palette, blend_palette
@@ -59,7 +59,7 @@ def __init__(self, variable: str | None = None):
             variable = self.__class__.__name__.lower()
         self.variable = variable
 
-    def default_scale(self, data: Series) -> ScaleSpec:
+    def default_scale(self, data: Series) -> Scale:
         """Given data, initialize appropriate scale class."""
         # TODO allow variable_type to be "boolean" if that's a scale?
         # TODO how will this handle data with units that can be treated as numeric
@@ -75,7 +75,7 @@ def default_scale(self, data: Series) -> ScaleSpec:
         else:
             return Nominal()
 
-    def infer_scale(self, arg: Any, data: Series) -> ScaleSpec:
+    def infer_scale(self, arg: Any, data: Series) -> Scale:
         """Given data and a scaling argument, initialize appropriate scale class."""
         # TODO put these somewhere external for validation
         # TODO putting this here won't pick it up if subclasses define infer_scale
@@ -86,7 +86,7 @@ def infer_scale(self, arg: Any, data: Series) -> ScaleSpec:
         if isinstance(arg, str):
             if any(arg.startswith(k) for k in trans_args):
                 # TODO validate numeric type? That should happen centrally somewhere
-                return Continuous(transform=arg)
+                return Continuous(trans=arg)
             else:
                 msg = f"Unknown magic arg for {self.variable} scale: '{arg}'."
                 raise ValueError(msg)
@@ -96,7 +96,7 @@ def infer_scale(self, arg: Any, data: Series) -> ScaleSpec:
             raise TypeError(msg)
 
     def get_mapping(
-        self, scale: ScaleSpec, data: Series
+        self, scale: Scale, data: Series
     ) -> Callable[[ArrayLike], ArrayLike]:
         """Return a function that maps from data domain to property range."""
         def identity(x):
@@ -176,7 +176,7 @@ def _inverse(self, values: ArrayLike) -> ArrayLike:
         """Transform applied to results of mapping that returns to native values."""
         return values
 
-    def infer_scale(self, arg: Any, data: Series) -> ScaleSpec:
+    def infer_scale(self, arg: Any, data: Series) -> Scale:
         """Given data and a scaling argument, initialize appropriate scale class."""
 
         # TODO infer continuous based on log/sqrt etc?
@@ -192,7 +192,7 @@ def infer_scale(self, arg: Any, data: Series) -> ScaleSpec:
             return Continuous(arg)
 
     def get_mapping(
-        self, scale: ScaleSpec, data: ArrayLike
+        self, scale: Scale, data: ArrayLike
     ) -> Callable[[ArrayLike], ArrayLike]:
         """Return a function that maps from data domain to property range."""
         if isinstance(scale, Nominal):
@@ -325,7 +325,7 @@ def infer_scale(self, arg: Any, data: Series) -> Nominal:
         return Nominal(arg)
 
     def get_mapping(
-        self, scale: ScaleSpec, data: Series,
+        self, scale: Scale, data: Series,
     ) -> Callable[[ArrayLike], list]:
         """Define mapping as lookup into list of object values."""
         order = getattr(scale, "order", None)
@@ -532,7 +532,7 @@ def has_alpha(x):
         else:
             return to_rgba_array(colors)[:, :3]
 
-    def infer_scale(self, arg: Any, data: Series) -> ScaleSpec:
+    def infer_scale(self, arg: Any, data: Series) -> Scale:
         # TODO when inferring Continuous without data, verify type
 
         # TODO need to rethink the variable type system
@@ -617,7 +617,7 @@ def mapping(x):
         return mapping
 
     def get_mapping(
-        self, scale: ScaleSpec, data: Series
+        self, scale: Scale, data: Series
     ) -> Callable[[ArrayLike], ArrayLike]:
         """Return a function that maps from data domain to color values."""
         # TODO what is best way to do this conditional?
@@ -690,13 +690,13 @@ def default_scale(self, data: Series) -> Nominal:
         """Given data, initialize appropriate scale class."""
         return Nominal()
 
-    def infer_scale(self, arg: Any, data: Series) -> ScaleSpec:
+    def infer_scale(self, arg: Any, data: Series) -> Scale:
         """Given data and a scaling argument, initialize appropriate scale class."""
         # TODO infer Boolean where possible?
         return Nominal(arg)
 
     def get_mapping(
-        self, scale: ScaleSpec, data: Series
+        self, scale: Scale, data: Series
     ) -> Callable[[ArrayLike], ArrayLike]:
         """Return a function that maps each data value to True or False."""
         # TODO categorical_order is going to return [False, True] for booleans,