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Certain padding values cause plots to overtake all other subplots #4144
Description
Related to #4124 there is a set of padding values that will produce strange behavior such that a single subplot takes over all others.
Some setup:
import numpy as np
import plotly.graph_objects as go
from plotly.subplots import make_subplots
line_x = np.arange(10)
line_y = line_x**2
What works:
n_subplots = 6
full_fig = make_subplots(
rows=n_subplots,
cols=1,
)
for row_idx in range(1, n_subplots+1):
full_fig.add_trace(go.Scatter(
x=line_x,
y=line_y,
showlegend=False,
), row=row_idx, col=1)
This produces 6 different subplots of the same line.
What doesn't work:
line_x = np.arange(10)
line_y = line_x**2
n_subplots = 8
padding_size = 0.1
row_heights = [0.1]*n_subplots
specs = []
for _ in range(n_subplots):
specs.append([{'b': padding_size/2., 't': padding_size/2.}])
full_fig = make_subplots(
rows=n_subplots,
cols=1,
row_heights=row_heights,
specs=specs,
)
for row_idx in range(1, n_subplots+1):
full_fig.add_trace(go.Scatter(
x=line_x,
y=line_y,
showlegend=False,
), row=row_idx, col=1)
Adding the padding and row heights now generates only a single plot.
Activity
emilykl commentedon Sep 1, 2026
Hi @stephenpardy, apologies this issue never got a timely response — I just wanted to add a note here that this (bad!) behavior is due to the fact that
bandtpadding values are interpreted in terms of paper fraction of the entire plot, not as a fraction of the cell itself.The explanation which gets a bit in the weeds...
make_subplotsalready adds a default vertical spacing of0.3 / nrowsspacing between each pair of subplots, also in units of plot fraction, which means that each subplot cell takes up(1-0.3/8*7)/8 ≈ 0.0922of the vertical plot area. (Passingrow_heightsdoesn't bypass the defaultvertical_spacing). As a result, adding a total of0.1units of plot fraction to each subplot exceeds the total of0.0922units of plot fraction allowed for the whole subplot, somake_subplotsfalls back to an unfortunate failure case of just defaulting to[0, 1]vertical domain for every subplot, resulting in the overlap where only the final subplot is visible.All that to say, this is a bad API and the most minimal change would be to adjust the spec validation
make_subplots()to catch this case, the way it does if you pass a really large value for the margin padding in specs. The whole subplot padding/spacing API should probably be improved as well, but that's a larger chunk of work.