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FIX: use data values in bar_label#31819

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timhoffm merged 1 commit into
matplotlib:mainfrom
rcomer:bar_label-int
Jun 4, 2026
Merged

FIX: use data values in bar_label#31819
timhoffm merged 1 commit into
matplotlib:mainfrom
rcomer:bar_label-int

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@rcomer rcomer commented Jun 4, 2026 •
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PR summary

This is a minor issue, but...

Currently it is not possible to format bar labels as integers, even if the original data are ints:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
bars = ax.bar(['foo', 'bar'], [5, 7])
labels = ax.bar_label(bars, fmt='N={:d}')

plt.show()
Traceback (most recent call last):
  File "/[path-to-git-repo]/matplotlib/lib/matplotlib/cbook.py", line 2546, in _auto_format_str
    return fmt % (value,)
           ~~~~^~~~~~~~~~
TypeError: not all arguments converted during string formatting

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/[path-to-script]/bar_label_example.py", line 5, in <module>
    labels = ax.bar_label(bars, fmt='N={:d}')
  File "/[path-to-git-repo]/matplotlib/lib/matplotlib/axes/_axes.py", line 2970, in bar_label
    lbl = cbook._auto_format_str(fmt, value)
  File "/[path-to-git-repo]/matplotlib/lib/matplotlib/cbook.py", line 2548, in _auto_format_str
    return fmt.format(value)
           ~~~~~~~~~~^^^^^^^
ValueError: Unknown format code 'd' for object of type 'float'

The values used are derived from the size of the rectangle, and are therefore always floats. However, the actual data values are also available in this loop, so I'm not clear why we don't directly use them. I wondered if it had to do with unit handling, but the data values on the container have already been processed as height or width within bar

matplotlib/lib/matplotlib/axes/_axes.py

Line 2517 in b825c6d

width = self._convert_dx(width, x0, x, self.convert_xunits)

matplotlib/lib/matplotlib/axes/_axes.py

Line 2523 in b825c6d

height = self._convert_dx(height, y0, y, self.convert_yunits)

matplotlib/lib/matplotlib/axes/_axes.py

Lines 2644 to 2647 in b825c6d

if orientation == 'vertical':
datavalues = height
else: # horizontal
datavalues = width

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story645 commented Jun 4, 2026

Good catch!

@story645 story645 added this to the v3.11.0 milestone Jun 4, 2026
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timhoffm approved these changes Jun 4, 2026
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Not using the original data is probably a historic implementation oversight. #15602 was created though many iterations and the datavalues were not originally part of the loop. They just came in via 21da4c1 and when that happened probably nobody thought about that this also simplifies and makes the value formatting more straightforward.

@timhoffm timhoffm merged commit bd14441 into matplotlib:main Jun 4, 2026
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@meeseeksmachine meeseeksmachine mentioned this pull request Jun 4, 2026
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rcomer commented Jun 4, 2026

Good catch!

I actually tripped over this one in my day job 😏

@rcomer rcomer deleted the bar_label-int branch June 4, 2026 20:58
@rcomer rcomer added the PR: bugfix Pull requests that fix identified bugs label Jun 4, 2026
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