Draw a separator or lines between subplots

Question

I have plot four subplots in one figure and they shares xaxis with each other.

However, there is no separator between those subplots. I want to draw a line between each of them. or is there any separator could be adopted in those subplots?

At least there should be separator between the subplots' axis. I think it should be looked as below figure.

\------------------------------------

  subplot1

\------------------------------------

  subplot2

\------------------------------------

  ...

\------------------------------------

Answer 1

If the axes/subplots have decorators like x labels or tick labels, it's not straight forward to find the correct position of the lines that should separate the subplots, such that they do not overlap with the texts.

One solution to this can be to get the extent of the axes including decorators and take the mean in between the bottom of the upper and the top of the lower extent.

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.transforms as mtrans

fig, axes = plt.subplots(3,2, squeeze=False)

for i, ax in enumerate(axes.flat):
    ax.plot([1,2])
    ax.set_title('Title ' + str(i+1))
    ax.set_xlabel('xaxis')
    ax.set_ylabel('yaxis')

# rearange the axes for no overlap
fig.tight_layout()

# Get the bounding boxes of the axes including text decorations
r = fig.canvas.get_renderer()
get_bbox = lambda ax: ax.get_tightbbox(r).transformed(fig.transFigure.inverted())
bboxes = np.array(list(map(get_bbox, axes.flat)), mtrans.Bbox).reshape(axes.shape)

#Get the minimum and maximum extent, get the coordinate half-way between those
ymax = np.array(list(map(lambda b: b.y1, bboxes.flat))).reshape(axes.shape).max(axis=1)
ymin = np.array(list(map(lambda b: b.y0, bboxes.flat))).reshape(axes.shape).min(axis=1)
ys = np.c_[ymax[1:], ymin[:-1]].mean(axis=1)

# Draw a horizontal lines at those coordinates
for y in ys:
    line = plt.Line2D([0,1],[y,y], transform=fig.transFigure, color="black")
    fig.add_artist(line)


plt.show()