How to add a frame to a seaborn heatmap figure in python ?

Example of how to add a frame to a seaborn heatmap figure in python

Plot a figure with seaborn heatmap

Example of how to plot a figure with seaborn heatmap

import seaborn as sns
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt


data = np.array([[25.55535942,  1.99598017,  9.78107706],
 [ 4.95758736, 39.68268716, 16.78109873],
 [ 0.45401194,  0.10003128,  0.6921669 ]])

df = pd.DataFrame(data=data)

fig = plt.figure(num=None, figsize=(10, 10), dpi=80, facecolor='w', edgecolor='k')

cmap = sns.cubehelix_palette(light=1, as_cmap=True)

res = sns.heatmap(df, annot=True, vmin=0.0, vmax=100.0, 
                  fmt='.2f', cmap=cmap, cbar_kws={"shrink": .82})

res.invert_yaxis()

plt.title('Seaborn heatmap - with frame')

plt.savefig('seaborn_heatmap_with_frame_and_cell_border_01.png')              
plt.show()

Add a frame to the figure

To add a frame a solution is to add the following lines:

for _, spine in res.spines.items():
    spine.set_visible(True)

in

import seaborn as sns
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt


data = np.array([[25.55535942,  1.99598017,  9.78107706],
 [ 4.95758736, 39.68268716, 16.78109873],
 [ 0.45401194,  0.10003128,  0.6921669 ]])

df = pd.DataFrame(data=data)

fig = plt.figure(num=None, figsize=(10, 10), dpi=80, facecolor='w', edgecolor='k')

cmap = sns.cubehelix_palette(light=1, as_cmap=True)

res = sns.heatmap(df, annot=True, vmin=0.0, vmax=100.0, 
                  fmt='.2f', cmap=cmap, cbar_kws={"shrink": .82})

res.invert_yaxis()

# make frame visible
for _, spine in res.spines.items():
    spine.set_visible(True)

plt.title('Seaborn heatmap - with frame')

plt.savefig('seaborn_heatmap_with_frame_01.png')              
plt.show()

Add cell borders

Another option is to use the arguments linewidths=0.1 and linecolor='gray':

import seaborn as sns
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt


data = np.array([[25.55535942,  1.99598017,  9.78107706],
 [ 4.95758736, 39.68268716, 16.78109873],
 [ 0.45401194,  0.10003128,  0.6921669 ]])

df = pd.DataFrame(data=data)

fig = plt.figure(num=None, figsize=(10, 10), dpi=80, facecolor='w', edgecolor='k')

cmap = sns.cubehelix_palette(light=1, as_cmap=True)

res = sns.heatmap(df, annot=True, vmin=0.0, vmax=100.0, 
                  fmt='.2f', cmap=cmap, cbar_kws={"shrink": .82},
                  linewidths=0.1, linecolor='gray')

res.invert_yaxis()

plt.title('Seaborn heatmap - with frame')

plt.savefig('seaborn_heatmap_with_frame_and_cell_border_01.png')              
plt.show()

References