Nested groups

fig.group() has no notion of nesting or hierarchy – it always draws one box, sized to the bounding rectangle of whichever axes it was given. This figure looks nested (an outer “All four” box visually containing two narrower ones, titles included) purely because that is what its own box happens to bound: within a plain 2x2 grid, Left pair/Right pair each group one 2x1 column, and All four separately groups all four axes. All three are otherwise completely independent, unrelated groups as far as plotpress is concerned – nothing links All four to the two narrower ones, or stops you from moving one axes out of a “child” group without touching the “parent” at all.

Two choices make every title land inside the outer box rather than alongside or past it:

• Left pair/Right pair take the one edge each actually reaches that the other doesn’t (left/right); All four takes bottom, the one edge neither of them uses – tight_layout() reserves title space per edge, not per group, so distinct edges avoid two titles fighting over one reservation.

• Margins are set by hand with subplots_adjust() instead of tight_layout(). All four’s own pad has to be wide enough to clear Left pair’s and Right pair’s titles, not just their axes – room tight_layout() never reserves on its own, since neither of those titles faces a figure edge it knows to budget for. Generous, explicit margins on every side give that pad somewhere to expand into without running off the canvas.

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import numpy as np
import plotpress

rng = np.random.default_rng(9)
x = np.linspace(0, 6, 13)
y = np.linspace(0, 6, 13)
X, Y = np.meshgrid(x, y)

fig, axes = plotpress.subplots(2, 2, figsize=(9, 8))
for r in range(2):
    for c in range(2):
        Z = np.sin(X * 0.6 + r) * np.cos(Y * 0.6 + c) + 0.05 * rng.standard_normal(X.shape)
        axes[r, c].pcolormesh(x, y, Z, cmap="cividis", vmin=-1.2, vmax=1.2)
        axes[r, c].tick_params(labelsize=6)

fig.group("Left pair", [axes[0, 0], axes[1, 0]], title_position="left", color="#2ca02c")
fig.group("Right pair", [axes[0, 1], axes[1, 1]], title_position="right", color="#9467bd")
fig.group("All four", list(axes.ravel()), title_position="bottom", color="black",
         pad=75.0)
fig.subplots_adjust(left=0.20, right=0.80, top=0.90, bottom=0.16,
                    wspace=0.30, hspace=0.30)