Row titles for matplotlib subplot

New in matplotlib 3.4.0

Row titles can now be implemented as subfigure suptitles:

The new subfigure feature allows creating virtual figures within figures with localized artists (e.g., colorbars and suptitles) that only pertain to each subfigure.

See how to plot subfigures for further details.

How to reproduce OP’s reference figure:

• Either Figure.subfigures (most straightforward)

  Create 3×1 fig.subfigures where each subfig gets its own 1×3 subfig.subplots and subfig.suptitle:

  fig = plt.figure(constrained_layout=True)
  fig.suptitle('Figure title')
  
  # create 3x1 subfigs
  subfigs = fig.subfigures(nrows=3, ncols=1)
  for row, subfig in enumerate(subfigs):
      subfig.suptitle(f'Subfigure title {row}')
  
      # create 1x3 subplots per subfig
      axs = subfig.subplots(nrows=1, ncols=3)
      for col, ax in enumerate(axs):
          ax.plot()
          ax.set_title(f'Plot title {col}')
  

• Or Figure.add_subfigure (onto existing subplots)

  If you already have 3×1 plt.subplots, then add_subfigure into the underlying gridspec. Again each subfig will get its own 1×3 subfig.subplots and subfig.suptitle:

  # create 3x1 subplots
  fig, axs = plt.subplots(nrows=3, ncols=1, constrained_layout=True)
  fig.suptitle('Figure title')
  
  # clear subplots
  for ax in axs:
      ax.remove()
  
  # add subfigure per subplot
  gridspec = axs[0].get_subplotspec().get_gridspec()
  subfigs = [fig.add_subfigure(gs) for gs in gridspec]
  
  for row, subfig in enumerate(subfigs):
      subfig.suptitle(f'Subfigure title {row}')
  
      # create 1x3 subplots per subfig
      axs = subfig.subplots(nrows=1, ncols=3)
      for col, ax in enumerate(axs):
          ax.plot()
          ax.set_title(f'Plot title {col}')
  

Output of either example (after some styling):