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fix: Fix flaky matplotlib-to-plotly conversion of touching bars (negative bargap) #5696

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fix: Fix flaky matplotlib-to-plotly conversion of touching bars (negative bargap) #5696

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4 changes: 3 additions & 1 deletion plotly/matplotlylib/mpltools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -269,7 +269,9 @@ def get_bar_gap(bar_starts, bar_ends, tol=1e-10):
gap0 = gaps[0]
uniform = all([abs(gap0 - gap) < tol for gap in gaps])
if uniform:
return gap0
# plotly's bargap must be in [0, 1]; clamp to guard against
# floating point noise (e.g. -8.9e-16 for touching bars)
return min(max(gap0, 0.0), 1.0)
Comment on lines +272 to +274

@camdecoster camdecoster Sep 24, 2026

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We need to normalize gap0 to calculate the correct bargap.

Suggested change
# plotly's bargap must be in [0, 1]; clamp to guard against
# floating point noise (e.g. -8.9e-16 for touching bars)
return min(max(gap0, 0.0), 1.0)
# Plotly's `bargap` is a fraction of the distance between bar positions, not a gap in data units
# so we need to normalize `gap0` with `bar_delta`
bar_delta = bar_starts[1] - bar_starts[0]
if bar_delta <= 0:
return None
# Clamp to guard against floating point noise, such as -8.9e-16 for touching bars
return min(max(gap0 / bar_delta, 0.0), 1.0)



def convert_rgba_array(color_list):
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13 changes: 13 additions & 0 deletions plotly/matplotlylib/tests/test_renderer.py
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Expand Up @@ -235,6 +235,19 @@ def test_semitransparent_axes_background_preserved():
assert plotly_fig.layout.plot_bgcolor == "rgba(26, 51, 76, 0.4)"


def test_histogram_converts():
"""Histograms must convert without error and keep bargap in plotly's
valid [0, 1] range; get_bar_gap can return a gap with floating point
noise for touching bars, which plotly rejects."""
fig, ax = plt.subplots()
ax.hist(np.random.randn(1000), 30)

plotly_fig = tls.mpl_to_plotly(fig)

assert len(plotly_fig.data) == 1
assert 0 <= plotly_fig.layout.bargap <= 1
Comment on lines +242 to +248

@camdecoster camdecoster Sep 24, 2026

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Let's make this test deterministic:

Suggested change
fig, ax = plt.subplots()
ax.hist(np.random.randn(1000), 30)
plotly_fig = tls.mpl_to_plotly(fig)
assert len(plotly_fig.data) == 1
assert 0 <= plotly_fig.layout.bargap <= 1
# Seed 0 makes the first gap slightly negative (-4.4e-16)
rng = np.random.RandomState(0)
fig, ax = plt.subplots()
ax.hist(rng.randn(10000), 30)
plotly_fig = tls.mpl_to_plotly(fig)
assert len(plotly_fig.data) == 1
assert plotly_fig.layout.bargap == 0



def test_line_color_is_valid_plotly_color():
"""Converted line colors are valid plotly color strings: plotly rejects
a space between 'rgba' and the opening parenthesis."""
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