From ab08bb508fa2bcc7fa3c2ae2fce8b9eaaf31829e Mon Sep 17 00:00:00 2001
From: Hanjin Liu <liuhanjin-sc@i.softbank.jp>
Date: Sat, 31 Aug 2024 22:49:59 +0900
Subject: [PATCH 1/6] fix legend item

---
 whitecanvas/layers/group/_collections.py | 27 +++++++++++-------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/whitecanvas/layers/group/_collections.py b/whitecanvas/layers/group/_collections.py
index a2146c01..894fb92d 100644
--- a/whitecanvas/layers/group/_collections.py
+++ b/whitecanvas/layers/group/_collections.py
@@ -79,6 +79,12 @@ def _connect_canvas(self, canvas: Canvas):
     def _disconnect_canvas(self, canvas: Canvas):
         return super()._disconnect_canvas(canvas)
 
+    def _as_legend_item(self):
+        """Use the first layer as the main legend item."""
+        if len(self._children) == 0:
+            return _legend.EmptyLegendItem()
+        return self._children[0]._as_legend_item()
+
 
 class LayerTuple(LayerContainer, Sequence[Layer]):
     def __getitem__(self, key: int | str) -> Layer:
@@ -141,16 +147,10 @@ def insert(self, n: int, layer: _L):
         self._ordering_indices.insert(n, len(self._ordering_indices))
         return None
 
-    def _as_legend_item(self):
-        """Use the first layer as the main legend item."""
-        if len(self) == 0:
-            return _legend.EmptyLegendItem()
-        return self[0]._as_legend_item()
-
+    # fmt: off
     if TYPE_CHECKING:
-
-        def iter_children(self) -> Iterator[_L]:
-            ...
+        def iter_children(self) -> Iterator[_L]: ...
+    # fmt: on
 
 
 _L0 = TypeVar("_L0", bound=Layer)
@@ -159,16 +159,13 @@ def iter_children(self) -> Iterator[_L]:
 
 class MainAndOtherLayers(LayerTuple, Generic[_L0, _L1]):
     @overload
-    def __getitem__(self, n: Literal[0]) -> _L0:
-        ...
+    def __getitem__(self, n: Literal[0]) -> _L0: ...
 
     @overload
-    def __getitem__(self, n: Literal[0]) -> _L1:
-        ...
+    def __getitem__(self, n: Literal[0]) -> _L1: ...
 
     @overload
-    def __getitem__(self, n: int) -> Layer:
-        ...
+    def __getitem__(self, n: int) -> Layer: ...
 
     def __getitem__(self, n):
         """The n-th layer."""

From 988eaf57776b94a305c21306f92095f64ceb8ac2 Mon Sep 17 00:00:00 2001
From: Hanjin Liu <liuhanjin-sc@i.softbank.jp>
Date: Sat, 31 Aug 2024 23:12:51 +0900
Subject: [PATCH 2/6] impl name filter

---
 whitecanvas/canvas/_base.py           |   8 +-
 whitecanvas/canvas/_joint.py          |  10 +-
 whitecanvas/layers/_primitive/line.py | 127 ++++++++++++++++++++++++++
 whitecanvas/utils/predicate.py        |   8 ++
 whitecanvas/utils/type_check.py       |   2 +
 5 files changed, 151 insertions(+), 4 deletions(-)
 create mode 100644 whitecanvas/utils/predicate.py

diff --git a/whitecanvas/canvas/_base.py b/whitecanvas/canvas/_base.py
index 9d80a638..8107889e 100644
--- a/whitecanvas/canvas/_base.py
+++ b/whitecanvas/canvas/_base.py
@@ -52,6 +52,7 @@
     Symbol,
 )
 from whitecanvas.utils.normalize import as_array_1d, normalize_xy
+from whitecanvas.utils.predicate import not_starts_with_underscore
 from whitecanvas.utils.type_check import is_real_number
 
 if TYPE_CHECKING:
@@ -99,7 +100,7 @@ def _draw_canvas(self):
         self._canvas()._plt_draw()
         self.events.drawn.emit()
 
-    def _coerce_name(self, name: str | None, default: str = "data") -> str:
+    def _coerce_name(self, name: str | None, default: str = "_data") -> str:
         if name is None:
             basename = default
             name = f"{default}-0"
@@ -743,6 +744,7 @@ def add_legend(
         *,
         location: Location | LocationStr = "top_right",
         title: str | None = None,
+        name_filter: Callable[[str], bool] = not_starts_with_underscore,
     ):
         """
         Add legend items to the canvas.
@@ -779,6 +781,8 @@ def add_legend(
             ```
         title : str, optional
             If given, title label will be added as the first legend item.
+        name_filter : callable, default not_starts_with_underscore
+            A callable that returns True if the name should be included in the legend.
         """
         if layers is None:
             layers = list(self.layers)
@@ -788,6 +792,8 @@ def add_legend(
 
         items = list[tuple[str, _legend.LegendItem]]()
         for layer in layers:
+            if not name_filter(layer.name):
+                continue
             if isinstance(layer, str):
                 items.append((layer, _legend.TitleItem()))
             elif isinstance(layer, _l.Layer):
diff --git a/whitecanvas/canvas/_joint.py b/whitecanvas/canvas/_joint.py
index aebb2c0d..ed99709a 100644
--- a/whitecanvas/canvas/_joint.py
+++ b/whitecanvas/canvas/_joint.py
@@ -3,6 +3,7 @@
 from abc import ABC, abstractmethod
 from typing import (
     TYPE_CHECKING,
+    Callable,
     Iterator,
     Literal,
     Sequence,
@@ -31,6 +32,7 @@
     OrientationLike,
     Symbol,
 )
+from whitecanvas.utils.predicate import not_starts_with_underscore
 
 if TYPE_CHECKING:
     from typing_extensions import Self
@@ -164,13 +166,15 @@ def _link_marginal_to_main(self, layer: _l.Layer, main: _l.Layer) -> None:
     def add_legend(
         self,
         layers: Sequence[str | _l.Layer] | None = None,
-        location: Location | LocationStr = "top_right",
         *,
+        location: Location | LocationStr = "top_right",
         title: str | None = None,
+        name_filter: Callable[[str], bool] = not_starts_with_underscore,
     ):
         """Add legend to the main canvas."""
-        self.main_canvas.add_legend(layers, location=location, title=title)
-        return None
+        return self.main_canvas.add_legend(
+            layers, location=location, title=title, name_filter=name_filter
+        )
 
     def add_markers(
         self,
diff --git a/whitecanvas/layers/_primitive/line.py b/whitecanvas/layers/_primitive/line.py
index 8cd083ea..cc5fb350 100644
--- a/whitecanvas/layers/_primitive/line.py
+++ b/whitecanvas/layers/_primitive/line.py
@@ -245,6 +245,26 @@ def with_xerr(
         antialias: bool | _Void = _void,
         capsize: float = 0,
     ) -> _lg.LabeledLine[Self]:
+        """
+        Add error bars parallel to the x-axis.
+
+        Parameters
+        ----------
+        err : array-like
+            The error values.
+        err_high : array-like, optional
+            The higher error values. If not given, use `err`.
+        color : color-like, optional
+            The error bar color. Use the line color by default.
+        width : float, optional
+            The error bar line width. Use the line width by default.
+        style : str, optional
+            The error bar line style. Use the line style by default.
+        antialias : bool, optional
+            Whether to use antialiasing. Use the line antialias by default.
+        capsize : float, default 0
+            The cap size of the error bars.
+        """
         from whitecanvas.layers._primitive import Errorbars
         from whitecanvas.layers.group import LabeledLine
 
@@ -279,6 +299,26 @@ def with_yerr(
         antialias: bool | _Void = _void,
         capsize: float = 0,
     ) -> _lg.LabeledLine[Self]:
+        """
+        Add error bars parallel to the y-axis.
+
+        Parameters
+        ----------
+        err : array-like
+            The error values.
+        err_high : array-like, optional
+            The higher error values. If not given, use `err`.
+        color : color-like, optional
+            The error bar color. Use the line color by default.
+        width : float, optional
+            The error bar line width. Use the line width by default.
+        style : str, optional
+            The error bar line style. Use the line style by default.
+        antialias : bool, optional
+            Whether to use antialiasing. Use the line antialias by default.
+        capsize : float, default 0
+            The cap size of the error bars.
+        """
         from whitecanvas.layers._primitive import Errorbars
         from whitecanvas.layers.group import LabeledLine
 
@@ -311,6 +351,22 @@ def with_xband(
         alpha: float = 0.3,
         hatch: str | Hatch = Hatch.SOLID,
     ) -> _lg.LineBand[Self]:
+        """
+        Add a x-oriented band region attached to the line.
+
+        Parameters
+        ----------
+        err : array-like
+            The error values.
+        err_high : array-like, optional
+            The higher error values. If not given, use `err`.
+        color : color-like, optional
+            The band color. Use the line color by default.
+        alpha : float, optional
+            The band alpha value.
+        hatch : str or Hatch, optional
+            The band hatch pattern.
+        """
         from whitecanvas.layers._primitive import Band
         from whitecanvas.layers.group import LineBand
 
@@ -338,6 +394,22 @@ def with_yband(
         alpha: float = 0.3,
         hatch: str | Hatch = Hatch.SOLID,
     ) -> _lg.LineBand[Self]:
+        """
+        Add a y-oriented band region attached to the line.
+
+        Parameters
+        ----------
+        err : array-like
+            The error values.
+        err_high : array-like, optional
+            The higher error values. If not given, use `err`.
+        color : color-like, optional
+            The band color. Use the line color by default.
+        alpha : float, optional
+            The band alpha value.
+        hatch : str or Hatch, optional
+            The band hatch pattern.
+        """
         from whitecanvas.layers._primitive import Band
         from whitecanvas.layers.group import LineBand
 
@@ -364,11 +436,27 @@ def with_xfill(
         alpha: float = 0.3,
         hatch: str | Hatch = Hatch.SOLID,
     ) -> _lg.LineBand[Self]:
+        """
+        Fill the region between line and the y-axis (x-direction).
+
+        Parameters
+        ----------
+        bottom : float, default 0.0
+            The bottom value of the fill region.
+        color : color-like, optional
+            The fill color. Use the line color by default.
+        alpha : float, optional
+            The fill alpha value.
+        hatch : str or Hatch, optional
+            The fill hatch pattern.
+        """
         from whitecanvas.layers._primitive import Band
         from whitecanvas.layers.group import LineBand
 
         if color is _void:
             color = self.color
+        if not is_real_number(bottom):
+            raise TypeError(f"Expected `bottom` to be a number, got {type(bottom)}")
         data = self.data
         x0 = np.full((data.x.size,), bottom)
         band = Band(
@@ -387,11 +475,27 @@ def with_yfill(
         alpha: float = 0.3,
         hatch: str | Hatch = Hatch.SOLID,
     ) -> _lg.LineBand[Self]:
+        """
+        Fill the region between line and the x-axis (y-direction).
+
+        Parameters
+        ----------
+        bottom : float, default 0.0
+            The bottom value of the fill region.
+        color : color-like, optional
+            The fill color. Use the line color by default.
+        alpha : float, optional
+            The fill alpha value.
+        hatch : str or Hatch, optional
+            The fill hatch pattern.
+        """
         from whitecanvas.layers._primitive import Band
         from whitecanvas.layers.group import LineBand
 
         if color is _void:
             color = self.color
+        if not is_real_number(bottom):
+            raise TypeError(f"Expected `bottom` to be a number, got {type(bottom)}")
         data = self.data
         y0 = np.full((data.y.size,), bottom)
         band = Band(
@@ -448,6 +552,29 @@ def with_text(
         anchor: str | Alignment = Alignment.BOTTOM_LEFT,
         family: str | None = None,
     ) -> _lg.LabeledLine:
+        """
+        Add texts to each data point.
+
+        Parameters
+        ----------
+        strings : list of str
+            Texts to be added.
+        color : ColorType, default "black"
+            Color of the text.
+        size : float, optional
+            Font size., by default 12
+        rotation : float, default 0.0
+            Text rotation angle in degree.
+        anchor : str or Alignment, default Alignment.BOTTOM_LEFT
+            Anchor point of the text.
+        family : str, optional
+            Font family.
+
+        Returns
+        -------
+        LabeledLine
+            The labeled line layer.
+        """
         from whitecanvas.layers import Errorbars
         from whitecanvas.layers.group import LabeledLine
 
diff --git a/whitecanvas/utils/predicate.py b/whitecanvas/utils/predicate.py
new file mode 100644
index 00000000..33b3078c
--- /dev/null
+++ b/whitecanvas/utils/predicate.py
@@ -0,0 +1,8 @@
+from __future__ import annotations
+
+
+def not_starts_with_underscore(name: str) -> bool:
+    return not name.startswith("_")
+
+
+not_starts_with_underscore.__repr__ = lambda: "<not starts with `_`>"
diff --git a/whitecanvas/utils/type_check.py b/whitecanvas/utils/type_check.py
index 3bc72535..062a34b8 100644
--- a/whitecanvas/utils/type_check.py
+++ b/whitecanvas/utils/type_check.py
@@ -14,10 +14,12 @@
 
 
 def is_not_array(x) -> bool:
+    """True if x is not an array."""
     return np.isscalar(x) or isinstance(x, Enum)
 
 
 def is_real_number(x) -> TypeGuard[float]:
+    """True if x is a real number."""
     return isinstance(x, (int, float, Real, np.number))
 
 

From a15393927d09df7bd4c4edfece952a355f3c4c45 Mon Sep 17 00:00:00 2001
From: Hanjin Liu <liuhanjin-sc@i.softbank.jp>
Date: Sat, 31 Aug 2024 23:50:16 +0900
Subject: [PATCH 3/6] fix legend title position

---
 whitecanvas/backend/matplotlib/canvas.py | 8 +++++++-
 whitecanvas/canvas/_base.py              | 4 ++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/whitecanvas/backend/matplotlib/canvas.py b/whitecanvas/backend/matplotlib/canvas.py
index d8c4afaf..74e0eae9 100644
--- a/whitecanvas/backend/matplotlib/canvas.py
+++ b/whitecanvas/backend/matplotlib/canvas.py
@@ -309,10 +309,16 @@ def _plt_make_legend(
         if artists:
             loc, bbox_to_anchor = _LEGEND_LOC_MAP[anchor]
             font_size = self._plt_get_xticks()._plt_get_size()
-            self._axes.legend(
+            leg = self._axes.legend(
                 artists, names, loc=loc, bbox_to_anchor=bbox_to_anchor,
                 prop={"size": font_size},
             )  # fmt: skip
+            for item, text in zip(leg.legend_handles, leg.texts):
+                if isinstance(item, plt.Rectangle):
+                    extent = item.get_window_extent(leg.figure.canvas.get_renderer())
+                    width = extent.width
+                    text.set_fontweight("bold")
+                    text.set_position((-1.5 * width, 0))
             if anchor.is_side:
                 self._axes.figure.tight_layout()
 
diff --git a/whitecanvas/canvas/_base.py b/whitecanvas/canvas/_base.py
index 8107889e..f6eeb347 100644
--- a/whitecanvas/canvas/_base.py
+++ b/whitecanvas/canvas/_base.py
@@ -792,11 +792,11 @@ def add_legend(
 
         items = list[tuple[str, _legend.LegendItem]]()
         for layer in layers:
-            if not name_filter(layer.name):
-                continue
             if isinstance(layer, str):
                 items.append((layer, _legend.TitleItem()))
             elif isinstance(layer, _l.Layer):
+                if not name_filter(layer.name):
+                    continue
                 items.append((layer.name, layer._as_legend_item()))
             else:
                 raise TypeError(f"Expected a list of layer or str, got {type(layer)}.")

From 1d5a015e2ef189d03cb6fbe6f5bd2bd7ecb211db Mon Sep 17 00:00:00 2001
From: Hanjin Liu <liuhanjin-sc@i.softbank.jp>
Date: Sat, 31 Aug 2024 23:55:28 +0900
Subject: [PATCH 4/6] minor updates

---
 tests/test_canvas.py           | 2 +-
 whitecanvas/__init__.py        | 2 +-
 whitecanvas/utils/predicate.py | 3 ---
 3 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/tests/test_canvas.py b/tests/test_canvas.py
index 6b9456d7..071ca78f 100644
--- a/tests/test_canvas.py
+++ b/tests/test_canvas.py
@@ -222,7 +222,7 @@ def test_legend(backend: str):
     if backend == "vispy":
         pytest.skip("vispy does not support legend")
     canvas = new_canvas(backend=backend)
-    canvas.add_line([0, 1, 2], [0, 1, 2], name="line")
+    canvas.add_line([0, 1, 2], [0, 1, 2])
     canvas.add_markers([0, 1, 2], [0, 1, 2], name="markers")
     canvas.add_bars([0, 1, 2], [0, 1, 2], name="bars")
     canvas.add_line([3, 4, 5], [1, 2, 1], name="plot").with_markers()
diff --git a/whitecanvas/__init__.py b/whitecanvas/__init__.py
index 99bbe728..653613be 100644
--- a/whitecanvas/__init__.py
+++ b/whitecanvas/__init__.py
@@ -1,4 +1,4 @@
-__version__ = "0.3.1"
+__version__ = "0.3.2"
 
 from whitecanvas import theme
 from whitecanvas.canvas import link_axes
diff --git a/whitecanvas/utils/predicate.py b/whitecanvas/utils/predicate.py
index 33b3078c..d5d2a657 100644
--- a/whitecanvas/utils/predicate.py
+++ b/whitecanvas/utils/predicate.py
@@ -3,6 +3,3 @@
 
 def not_starts_with_underscore(name: str) -> bool:
     return not name.startswith("_")
-
-
-not_starts_with_underscore.__repr__ = lambda: "<not starts with `_`>"

From 87bec9f151b7e46cfe2add6f0aa03deca452db40 Mon Sep 17 00:00:00 2001
From: Hanjin Liu <liuhanjin-sc@i.softbank.jp>
Date: Sun, 8 Sep 2024 07:14:40 +0900
Subject: [PATCH 5/6] update mkdocs versions

---
 pyproject.toml | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 49f45748..9b11c001 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -72,11 +72,11 @@ testing = [
 
 docs = [
   "mkdocs",
-  "mkdocs-autorefs==0.5.0",
-  "mkdocs-material==9.5.2",
+  "mkdocs-autorefs==1.0.1",
+  "mkdocs-material==9.5.23",
   "mkdocs-material-extensions==1.3.1",
-  "mkdocstrings==0.24.0",
-  "mkdocstrings-python==1.7.5",
+  "mkdocstrings==0.25.2",
+  "mkdocstrings-python==1.10.8",
   "mkdocs-gen-files",
   "matplotlib>=3.8.2",
   "imageio>=2.9.0",

From 87babb7087ea9ef40c2a8fd6815b44016a4b56a3 Mon Sep 17 00:00:00 2001
From: Hanjin Liu <liuhanjin-sc@i.softbank.jp>
Date: Sun, 8 Sep 2024 07:41:45 +0900
Subject: [PATCH 6/6] fix warnings

---
 tests/test_logics.py                     |  8 ++++
 whitecanvas/backend/pyqtgraph/_labels.py |  2 +-
 whitecanvas/canvas/_namespaces.py        |  4 +-
 whitecanvas/layers/_mixin.py             |  4 +-
 whitecanvas/layers/_primitive/line.py    | 51 ++++++++++++++++--------
 5 files changed, 48 insertions(+), 21 deletions(-)

diff --git a/tests/test_logics.py b/tests/test_logics.py
index 2720483d..6f76bf5b 100644
--- a/tests/test_logics.py
+++ b/tests/test_logics.py
@@ -45,6 +45,14 @@ def test_kde():
     layer.band_width
     layer.band_width = 0.5
 
+def test_line_with_methods():
+    canvas = new_canvas(backend="mock")
+    line = canvas.add_line([1, 2], [4, 5])
+    with pytest.raises(TypeError):
+        line.with_xband([1, 1], alpha=[1, 2])
+        line.with_yfill([0, 1])
+        line.with_yfill(0.1, alpha=[1, 2])
+
 def test_hover_template():
     canvas = new_canvas(backend="mock")
     layer = canvas.add_markers([1, 2, 3], [4, 5, 6])
diff --git a/whitecanvas/backend/pyqtgraph/_labels.py b/whitecanvas/backend/pyqtgraph/_labels.py
index a6530229..1f81eacf 100644
--- a/whitecanvas/backend/pyqtgraph/_labels.py
+++ b/whitecanvas/backend/pyqtgraph/_labels.py
@@ -92,7 +92,7 @@ def _plt_set_text(self, text: str):
         self._get_axis().setLabel(text, **self._css)
 
     def _plt_get_color(self):
-        return np.array(Color(self._css["color"]))
+        return np.fromiter(Color(self._css["color"]), dtype=np.float32)
 
     def _plt_set_color(self, color):
         css = self._css.copy()
diff --git a/whitecanvas/canvas/_namespaces.py b/whitecanvas/canvas/_namespaces.py
index a3c2a04f..9a03d098 100644
--- a/whitecanvas/canvas/_namespaces.py
+++ b/whitecanvas/canvas/_namespaces.py
@@ -122,7 +122,7 @@ def color(self):
 
     @color.setter
     def color(self, color):
-        self._get_object()._plt_set_color(np.array(Color(color)))
+        self._get_object()._plt_set_color(np.fromiter(Color(color), dtype=np.float32))
 
     @property
     def size(self) -> float:
@@ -333,7 +333,7 @@ def color(self):
 
     @color.setter
     def color(self, color):
-        self._get_object()._plt_set_color(np.array(Color(color)))
+        self._get_object()._plt_set_color(np.fromiter(Color(color), dtype=np.float32))
         self._draw_canvas()
 
     @property
diff --git a/whitecanvas/layers/_mixin.py b/whitecanvas/layers/_mixin.py
index a9617c1d..5c48569a 100644
--- a/whitecanvas/layers/_mixin.py
+++ b/whitecanvas/layers/_mixin.py
@@ -722,7 +722,7 @@ def _make_sure_hatch_visible(self):
         _is_no_width = self.edge.width == 0
         if isinstance(self._edge_namespace, MultiEdge):
             if np.any(_is_no_width):
-                ec = np.array(get_theme().foreground_color, dtype=np.float32)
+                ec = np.fromiter(get_theme().foreground_color, dtype=np.float32)
                 self.edge.width = np.where(_is_no_width, 1, self.edge.width)
                 ec_old = self.edge.color
                 ec_old[_is_no_width] = ec[np.newaxis]
@@ -848,7 +848,7 @@ def __init__(self):
     def _make_sure_hatch_visible(self):
         _is_no_width = self.edge.width == 0
         if np.any(_is_no_width):
-            ec = np.array(get_theme().foreground_color, dtype=np.float32)
+            ec = np.fromiter(get_theme().foreground_color, dtype=np.float32)
             self.edge.width = np.where(_is_no_width, 1, self.edge.width)
             ec_old = self.edge.color
             ec_old[_is_no_width] = ec[np.newaxis]
diff --git a/whitecanvas/layers/_primitive/line.py b/whitecanvas/layers/_primitive/line.py
index cc5fb350..d7d42e31 100644
--- a/whitecanvas/layers/_primitive/line.py
+++ b/whitecanvas/layers/_primitive/line.py
@@ -370,10 +370,7 @@ def with_xband(
         from whitecanvas.layers._primitive import Band
         from whitecanvas.layers.group import LineBand
 
-        if err_high is None:
-            err_high = err
-        if color is _void:
-            color = self.color
+        err, err_high, color, alpha = _norm_band_args(self, err, err_high, color, alpha)
         data = self.data
         _x, _y0 = self._data_to_backend_data(XYData(data.y, data.x - err))
         _, _y1 = self._data_to_backend_data(XYData(data.y, data.x + err_high))
@@ -413,10 +410,7 @@ def with_yband(
         from whitecanvas.layers._primitive import Band
         from whitecanvas.layers.group import LineBand
 
-        if err_high is None:
-            err_high = err
-        if color is _void:
-            color = self.color
+        err, err_high, color, alpha = _norm_band_args(self, err, err_high, color, alpha)
         data = self.data
         _x, _y0 = self._data_to_backend_data(XYData(data.x, data.y - err))
         _, _y1 = self._data_to_backend_data(XYData(data.x, data.y + err_high))
@@ -453,10 +447,7 @@ def with_xfill(
         from whitecanvas.layers._primitive import Band
         from whitecanvas.layers.group import LineBand
 
-        if color is _void:
-            color = self.color
-        if not is_real_number(bottom):
-            raise TypeError(f"Expected `bottom` to be a number, got {type(bottom)}")
+        bottom, color, alpha = _norm_fill_args(self, bottom, color, alpha)
         data = self.data
         x0 = np.full((data.x.size,), bottom)
         band = Band(
@@ -492,10 +483,7 @@ def with_yfill(
         from whitecanvas.layers._primitive import Band
         from whitecanvas.layers.group import LineBand
 
-        if color is _void:
-            color = self.color
-        if not is_real_number(bottom):
-            raise TypeError(f"Expected `bottom` to be a number, got {type(bottom)}")
+        bottom, color, alpha = _norm_fill_args(self, bottom, color, alpha)
         data = self.data
         y0 = np.full((data.y.size,), bottom)
         band = Band(
@@ -507,6 +495,37 @@ def with_yfill(
         return LineBand(self, band, name=old_name)
 
 
+def _norm_band_args(
+    self: _SingleLine,
+    err: ArrayLike1D,
+    err_high: ArrayLike1D | None,
+    color: ColorType | _Void,
+    alpha: float,
+) -> tuple[ArrayLike1D, ArrayLike1D, ColorType, float]:
+    if err_high is None:
+        err_high = err
+    if color is _void:
+        color = self.color
+    if not is_real_number(alpha):
+        raise TypeError(f"Expected `alpha` to be a number, got {type(alpha)}")
+    return err, err_high, color, alpha
+
+
+def _norm_fill_args(
+    self: _SingleLine,
+    bottom: float,
+    color: ColorType | _Void,
+    alpha: float,
+) -> tuple[float, ColorType, float]:
+    if color is _void:
+        color = self.color
+    if not is_real_number(bottom):
+        raise TypeError(f"Expected `bottom` to be a number, got {type(bottom)}")
+    if not is_real_number(alpha):
+        raise TypeError(f"Expected `alpha` to be a number, got {type(alpha)}")
+    return bottom, color, alpha
+
+
 class Line(_SingleLine):
     _backend_class_name = "MonoLine"
     events: LineLayerEvents