Matplotlib.axes.Axes.set_ylabel() in Python

import matplotlib.pyplot as plt
import numpy as np
 
t = np.arange(0.01, 5.0, 0.01)
s = np.exp(-t)
 
fig, ax = plt.subplots()
 
ax.plot(t, s)
ax.set_ylim(1, 0)
ax.set_ylabel('Display Y-axis Label', 
              fontweight ='bold')
ax.grid(True)
 
ax.set_title('matplotlib.axes.Axes.set_ylabel() \
Examples\n', fontsize = 14, fontweight ='bold')
plt.show()

#Implementation of matplotlib function
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.cbook as cbook
 
with cbook.get_sample_data('goog.npz') as datafile:
    price_data = np.load(datafile)['price_data'].view(np.recarray)
    
# get the most recent 250 
# trading days
price_data = price_data[-250:]  
 
delta1 = np.diff(price_data.adj_close) / price_data.adj_close[:-1]
 
volume = (25 * price_data.volume[:-2] / price_data.volume[0])**(2.2)
close = (0.03 * price_data.close[:-2] / 0.03 * price_data.open[:-2])**2
 
fig, ax = plt.subplots()
ax.scatter(delta1[:-1], delta1[1:],
           c=close, s=volume,
           alpha=0.5)
 
ax.set_ylabel(r'Y-axis contains $\Delta_{i+1}$ values',
              fontweight='bold')
ax.grid(True)
fig.suptitle('matplotlib.axes.Axes.set_ylabel() Examples\n',
             fontsize=14, fontweight='bold')
plt.show()