bar labeling in matplotlib

import matplotlib.pyplot as plt  
  
   
# creating the dataset 
data = {'C':20, 'C++':15, 'Java':30,  
        'Python':35} 
courses = list(data.keys()) 
values = list(data.values()) 
   

fig = plt.figure(figsize = (5, 5)) 
  
# creating the bar plot 
plt.bar(courses, values, color ='green',  
        width = 0.4) 
  
plt.xlabel("Courses offered") 
plt.ylabel("No. of students enrolled") 
plt.title("Students enrolled in different courses") 
plt.show() 

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_axes([0,0,1,1])
langs = ['C', 'C++', 'Java', 'Python', 'PHP']
students = [23,17,35,29,12]
ax.bar(langs,students)
plt.show()

import matplotlib.pyplot as plt
%matplotlib inline
plt.style.use('ggplot')

x = ['Nuclear', 'Hydro', 'Gas', 'Oil', 'Coal', 'Biofuel']
energy = [5, 6, 15, 22, 24, 8]

x_pos = [i for i, _ in enumerate(x)]

plt.bar(x_pos, energy, color='green')
plt.xlabel("Energy Source")
plt.ylabel("Energy Output (GJ)")
plt.title("Energy output from various fuel sources")

plt.xticks(x_pos, x)

plt.show()