Unequal padding on each side of a group

pad is a single number on every other example in this gallery – the same clearance on all four sides. It also accepts a (left, right, top, bottom) sequence for unequal padding, useful exactly when a group’s own edges don’t all mean the same thing: the two groups below sit right next to each other, sharing one boundary in the middle of the figure and each carrying a title on their own outer top edge.

A single scalar pad big enough for the title clearance both groups need would also push their shared inner boundary apart by the same amount, even though nothing is there to clear – wasted canvas, and the two groups read as farther apart than they should. Tightening just that one side (left for “After”, right for “Before”) while keeping the title-facing top generous does what a single number can’t: the two boxes visibly touch in the middle, without either title crowding its own plots.

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import numpy as np
import plotpress

rng = np.random.default_rng(3)
x = np.linspace(0, 6, 17)
y = np.linspace(0, 4, 13)
X, Y = np.meshgrid(x, y)

fig, axes = plotpress.subplots(2, 4, figsize=(12, 6))
for r in range(2):
    for c in range(4):
        phase = c * 0.5
        Z = np.sin(X + phase - r) * np.cos(Y - phase) + 0.05 * rng.standard_normal(X.shape)
        axes[r, c].pcolormesh(x, y, Z, cmap="viridis", vmin=-1.2, vmax=1.2)
        axes[r, c].tick_params(labelsize=6)

# (left, right, top, bottom) -- tight on the side facing the other group,
# generous everywhere else, including the top each title needs.
fig.group("Before", list(axes[:, 0:2].ravel()), title_position="top",
         color="#1f77b4", pad=(20.0, 4.0, 24.0, 8.0))
fig.group("After", list(axes[:, 2:4].ravel()), title_position="top",
         color="#d62728", pad=(4.0, 20.0, 24.0, 8.0))

# The shared boundary is interior to the grid and neither title faces it,
# so tight_layout() won't widen it on its own -- group_spacing() reserves
# just enough room for the two tightened (4px) inner edges to clear each
# other without colliding.
fig.group_spacing(wspace=10.0)
fig.tight_layout()