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Improve default formatter for Slider values. #17077

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Merged
merged 1 commit into from
Apr 9, 2020
Merged

Improve default formatter for Slider values. #17077

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8 changes: 8 additions & 0 deletions doc/api/api_changes_3.3/behaviour.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -155,3 +155,11 @@ support for it will be dropped in a future Matplotlib release.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Previously, keyword arguments were silently ignored when no positional
arguments were given.

Default slider formatter
~~~~~~~~~~~~~~~~~~~~~~~~
The default method used to format `.Slider` values has been changed to use a
`.ScalarFormatter` adapted the slider values limits. This should ensure that
values are displayed with an appropriate number of significant digits even if
they are much smaller or much bigger than 1. To restore the old behavior,
explicitly pass a "%1.2f" as the *valfmt* parameter to `.Slider`.
38 changes: 29 additions & 9 deletions lib/matplotlib/widgets.py
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Expand Up @@ -16,7 +16,7 @@
import numpy as np

import matplotlib as mpl
from . import cbook
from . import cbook, ticker
from .lines import Line2D
from .patches import Circle, Rectangle, Ellipse
from .transforms import blended_transform_factory
Expand Down Expand Up @@ -256,7 +256,8 @@ class Slider(AxesWidget):
val : float
Slider value.
"""
def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt='%1.2f',

def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
closedmin=True, closedmax=True, slidermin=None,
slidermax=None, dragging=True, valstep=None,
orientation='horizontal', **kwargs):
Expand All @@ -278,8 +279,9 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt='%1.2f',
valinit : float, default: 0.5
The slider initial position.

valfmt : str, default: "%1.2f"
Used to format the slider value, fprint format string.
valfmt : str, default: None
%-format string used to format the slider value. If None, a
`.ScalarFormatter` is used instead.

closedmin : bool, default: True
Whether the slider interval is closed on the bottom.
Expand Down Expand Up @@ -347,13 +349,22 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt='%1.2f',
self.poly = ax.axvspan(valmin, valinit, 0, 1, **kwargs)
self.vline = ax.axvline(valinit, 0, 1, color='r', lw=1)

self.valfmt = valfmt
ax.set_yticks([])
if orientation == 'vertical':
ax.set_ylim((valmin, valmax))
axis = ax.yaxis
else:
ax.set_xlim((valmin, valmax))
axis = ax.xaxis

self.valfmt = valfmt
self._fmt = axis.get_major_formatter()
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Is this attribute is introduced here? If so, let's call it

Suggested change
self._fmt = axis.get_major_formatter()
self._formatter = axis.get_major_formatter()

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fmt for format(ter) is a pretty standard abbreviation, and this avoids an awkward linebreak a bit later which also helps from a legibility PoV. OTOH I don't really want to argue too much over this so if you are sure you prefer _formatter, let me know and I'll do the change (yes, it's a new attribute, so we can call it however we want).

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If I see fmt I expand to format in my mind, but I do not expand to formatter. OTOH, this isn't really a big deal here.

if not isinstance(self._fmt, ticker.ScalarFormatter):
self._fmt = ticker.ScalarFormatter()
self._fmt.set_axis(axis)
self._fmt.set_useOffset(False) # No additive offset.

ax.set_xticks([])
ax.set_yticks([])
ax.set_navigate(False)

self.connect_event('button_press_event', self._update)
Expand All @@ -365,7 +376,7 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt='%1.2f',
verticalalignment='bottom',
horizontalalignment='center')

self.valtext = ax.text(0.5, -0.02, valfmt % valinit,
self.valtext = ax.text(0.5, -0.02, self._format(valinit),
transform=ax.transAxes,
verticalalignment='top',
horizontalalignment='center')
Expand All @@ -374,7 +385,7 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt='%1.2f',
verticalalignment='center',
horizontalalignment='right')

self.valtext = ax.text(1.02, 0.5, valfmt % valinit,
self.valtext = ax.text(1.02, 0.5, self._format(valinit),
transform=ax.transAxes,
verticalalignment='center',
horizontalalignment='left')
Expand Down Expand Up @@ -435,6 +446,15 @@ def _update(self, event):
if val not in [None, self.val]:
self.set_val(val)

def _format(self, val):
"""Pretty-print *val*."""
if self.valfmt is not None:
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.
return s + self._fmt.get_offset()
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This will result in 3e-8 to be shown as 31e-8.

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oops, I had axes.formatter.usemathtext in my rcdefaults, we just need to force that here...


def set_val(self, val):
"""
Set slider value to *val*
Expand All @@ -451,7 +471,7 @@ def set_val(self, val):
xy[2] = val, 1
xy[3] = val, 0
self.poly.xy = xy
self.valtext.set_text(self.valfmt % val)
self.valtext.set_text(self._format(val))
if self.drawon:
self.ax.figure.canvas.draw_idle()
self.val = val
Expand Down