Add external margins with constrained layout?

Question

When generating a figure to save to a pdf file, I'd like to adjust the positioning of the figure relative to the edges of the page, for example to add an inch margin along all sides. As far as I can tell, the solutions to do this (for example, in this question) either:

1. don't work with constrained_layout mode -- applying plt.subplots_adjust() after creating the figure but prior to fig.savefig() messes up the constrained layout
2. don't actually quantitatively adjust the positioning of the figure -- adding bbox_inches="tight" or pad=-1 don't seem to do anything meaningful

Is there a straightforward way to adjust external margins of a constrained layout figure?

For example:

fig = plt.figure(constrained_layout=True, figsize=(11, 8.5))

page_grid = gridspec.GridSpec(nrows=2, ncols=1, figure=fig)

# this doesn't appear to do anything with constrained_layout=True
page_grid.update(left=0.2, right=0.8, bottom=0.2, top=0.8)

top_row_grid = gridspec.GridSpecFromSubplotSpec(1, 3, subplot_spec=page_grid[0])
for i in range(3):
    ax = fig.add_subplot(top_row_grid[:, i], aspect="equal")

n_bottom_row_plots = 10
qc_grid = gridspec.GridSpecFromSubplotSpec(1, n_bottom_row_plots, subplot_spec=page_grid[1])
for i, metric in enumerate(range(n_bottom_row_plots)):
    ax = fig.add_subplot(qc_grid[:, i])
    plt.plot(np.arange(5), np.arange(5))

fig.suptitle("my big label", fontweight="bold", fontsize="x-large", y=0.9)

# this ruins the constrained layout
# plt.subplots_adjust(left=0.2,right=0.8, bottom=0.2, top=0.8)

fig.savefig("temp.png", facecolor="coral")

Yields the following (I'd like to see more coral around the edges!):

Answer 1

Have you tried using the constrained layout padding option?

fig.set_constrained_layout_pads(w_pad=4./72., h_pad=4./72.,
            hspace=0./72., wspace=0./72.)

While this might help with spacing, the constrained layout will restrict the amount of object that you can add to the defined space.

''' Here is the modified code '''

import matplotlib.pyplot as plt
import matplotlib.colors as mcolors
import matplotlib.gridspec as gridspec
import numpy as np


fig = plt.figure(constrained_layout=True, figsize=(11, 8.5))
fig.set_constrained_layout_pads(w_pad=2./12., h_pad=4./12.,
            hspace=0., wspace=0.)
page_grid = gridspec.GridSpec(nrows=2, ncols=1, figure=fig)

fig.suptitle("My BIG Label", fontweight="bold", fontsize="x-large", y=0.98)


# this doesn't appear to do anything with constrained_layout=True
page_grid.update(left=0.2, right=0.8, bottom=0.2, top=0.8)

top_row_grid = gridspec.GridSpecFromSubplotSpec(1, 3, subplot_spec=page_grid[0])
for i in range(3):
    ax = fig.add_subplot(top_row_grid[:, i], aspect="equal")

n_bottom_row_plots = 10
qc_grid = gridspec.GridSpecFromSubplotSpec(1, n_bottom_row_plots, subplot_spec=page_grid[1])
for i, metric in enumerate(range(n_bottom_row_plots)):
    ax = fig.add_subplot(qc_grid[:, i])
    plt.plot(np.arange(5), np.arange(5))


# this ruins the constrained layout
# plt.subplots_adjust(left=0.2,right=0.8, bottom=0.2, top=0.8)

fig.savefig("temp.png", facecolor="coral")