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{,Range}Slider: accept callable valfmt arguments #30362

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Merged
merged 3 commits into from
Aug 7, 2025
Merged

{,Range}Slider: accept callable valfmt arguments #30362

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95cf154
widgets.pyi: Fix SliderBase's valfmt type
doronbehar Aug 7, 2025
4cdc046
{,Range}Slider: accept callable valfmt arguments
doronbehar Jul 27, 2025
b6d7441
{,Range}Slider: Add release notes for valfmt arguments
doronbehar Aug 5, 2025
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6 changes: 6 additions & 0 deletions doc/users/next_whats_new/sliders_callable_valfmt.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
Callable *valfmt* for ``Slider`` and ``RangeSlider``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In addition to the existing %-format string, the *valfmt* parameter of
`~.matplotlib.widgets.Slider` and `~.matplotlib.widgets.RangeSlider` now
also accepts a callable of the form ``valfmt(val: float) -> str``.
23 changes: 16 additions & 7 deletions lib/matplotlib/widgets.py
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Original file line number Diff line number Diff line change
Expand Up @@ -364,8 +364,9 @@ def __init__(self, ax, label, valmin, valmax, *, valinit=0.5, valfmt=None,
The slider initial position.

valfmt : str, default: None
%-format string used to format the slider value. If None, a
`.ScalarFormatter` is used instead.
The way to format the slider value. If a string, it must be in %-format.
If a callable, it must have the signature ``valfmt(val: float) -> str``.
If None, a `.ScalarFormatter` is used.

closedmin : bool, default: True
Whether the slider interval is closed on the bottom.
Expand Down Expand Up @@ -547,7 +548,10 @@ def _update(self, event):
def _format(self, val):
"""Pretty-print *val*."""
if self.valfmt is not None:
return self.valfmt % val
if callable(self.valfmt):
return self.valfmt(val)
else:
return self.valfmt % val
else:
_, s, _ = self._fmt.format_ticks([self.valmin, val, self.valmax])
# fmt.get_offset is actually the multiplicative factor, if any.
Expand Down Expand Up @@ -644,9 +648,11 @@ def __init__(
The initial positions of the slider. If None the initial positions
will be at the 25th and 75th percentiles of the range.

valfmt : str, default: None
%-format string used to format the slider values. If None, a
`.ScalarFormatter` is used instead.
valfmt : str or callable, default: None
The way to format the range's minimal and maximal values. If a
string, it must be in %-format. If a callable, it must have the
signature ``valfmt(val: float) -> str``. If None, a
`.ScalarFormatter` is used.

closedmin : bool, default: True
Whether the slider interval is closed on the bottom.
Expand Down Expand Up @@ -890,7 +896,10 @@ def _update(self, event):
def _format(self, val):
"""Pretty-print *val*."""
if self.valfmt is not None:
return f"({self.valfmt % val[0]}, {self.valfmt % val[1]})"
if callable(self.valfmt):
return f"({self.valfmt(val[0])}, {self.valfmt(val[1])})"
else:
return f"({self.valfmt % val[0]}, {self.valfmt % val[1]})"
else:
_, s1, s2, _ = self._fmt.format_ticks(
[self.valmin, *val, self.valmax]
Expand Down
6 changes: 3 additions & 3 deletions lib/matplotlib/widgets.pyi
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Expand Up @@ -64,7 +64,7 @@ class SliderBase(AxesWidget):
valmax: float
valstep: float | ArrayLike | None
drag_active: bool
valfmt: str
valfmt: str | Callable[[float], str] | None
def __init__(
self,
ax: Axes,
Expand All @@ -73,7 +73,7 @@ class SliderBase(AxesWidget):
closedmax: bool,
valmin: float,
valmax: float,
valfmt: str,
valfmt: str | Callable[[float], str] | None,
dragging: Slider | None,
valstep: float | ArrayLike | None,
) -> None: ...
Expand Down Expand Up @@ -130,7 +130,7 @@ class RangeSlider(SliderBase):
valmax: float,
*,
valinit: tuple[float, float] | None = ...,
valfmt: str | None = ...,
valfmt: str | Callable[[float], str] | None = ...,
closedmin: bool = ...,
closedmax: bool = ...,
dragging: bool = ...,
Expand Down
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