How to add black border to matplotlib 2.0 `ax` object In Python 3?

You probably want ax.spines.set_color()

These will give you a broad range of options for custom solutions:

ax.spines['bottom'].set_color('0.5')
ax.spines['top'].set_color(None)
ax.spines['right'].set_color('0.5')
ax.spines['left'].set_color(None)
ax.patch.set_facecolor('0.1')
plt.grid(b=True, which='major', color='0.2', linestyle='-')
plt.grid(b=True, which='minor', color='0.2', linestyle='-')
ax.tick_params(axis='x', colors='0.7', which='both')
ax.tick_params(axis='y', colors='0.7', which='both')
ax.yaxis.label.set_color('0.9')
ax.xaxis.label.set_color('0.9')
ax.margins(0.5)
fig.patch.set_facecolor('0.15')

For more details see: http://matplotlib.org/api/spines_api.html

The difference between the seaborn-whitegrid and the seaborn-white styles are

seaborn-whitegrid

axes.grid: True
axes.edgecolor: .8
axes.linewidth: 1

seaborn-white

axes.grid: False
axes.edgecolor: .15
axes.linewidth: 1.25

The following will thus provide identical plots:

import matplotlib.pyplot as plt
import pandas as pd
import numpy  as np
from collections import *

Se_data = pd.Series(Counter(np.random.randint(0,10,100)))
with plt.style.context("seaborn-whitegrid"):
    plt.rcParams["axes.edgecolor"] = "0.15"
    plt.rcParams["axes.linewidth"]  = 1.25
    fig, ax = plt.subplots()
    Se_data.plot(kind="barh", ax=ax, title="No Border")
with plt.style.context("seaborn-white"):
    plt.rcParams["axes.grid"] = True
    fig, ax = plt.subplots()
    Se_data.plot(kind="barh", ax=ax, title="With Border")

Take a look at this. What you're looking for are these two lines:

ax.patch.set_edgecolor('black')  

ax.patch.set_linewidth('1')