matplotlib - How to write text above the bars on a bar plot (Python)?

Question

I have this graph: I want to write the count above each column. These values are in the first and second lists. Can you help me solve this problem? I tried something without success.

This is the code for the graph:

countListFast = [1492.0, 497.0, 441.0, 218.0, 101.0, 78.0, 103.0]
countListSlow = [1718.0, 806.0, 850.0, 397.0, 182.0, 125.0, 106.0]

errorRateListOfFast = ['9.09', '9.09', '9.38', '9.40', '7.89', '8.02', '10.00']
errorRateListOfSlow = ['10.00', '13.04', '14.29', '12.50', '14.29', '14.53', '11.11']

opacity = 0.4
bar_width = 0.35

plt.xlabel('Tasks')
plt.ylabel('Error Rate')
plt.xticks(range(len(errorRateListOfFast)),('[10-20)', '[20-30)', '[30-50)', '[50-70)','[70-90)', '[90-120)', ' [120 < )'), rotation=30)
        plt.bar(np.arange(len(errorRateListOfFast))+ bar_width, errorRateListOfFast, bar_width, align='center', alpha=opacity, color='b', label='Fast <= 6 sec.')
plt.bar(range(len(errorRateListOfSlow)), errorRateListOfSlow, bar_width, align='center', alpha=opacity, color='r', label='Slower > 6 sec.')
plt.legend()
plt.tight_layout()
plt.show()

Answer 1

plt.bar() returns a list of rectangles that can be used to position suitable text above each of the bars as follows:

import matplotlib.pyplot as plt
import numpy as np

errorRateListOfFast = ['9.09', '9.09', '9.38', '9.40', '7.89', '8.02', '10.00']
errorRateListOfSlow = ['10.00', '13.04', '14.29', '12.50', '14.29', '14.53', '11.11']

# Convert to floats
errorRateListOfFast = [float(x) for x in errorRateListOfFast]
errorRateListOfSlow = [float(x) for x in errorRateListOfSlow]

opacity = 0.4
bar_width = 0.35

plt.xlabel('Tasks')
plt.ylabel('Error Rate')

plt.xticks(range(len(errorRateListOfFast)),('[10-20)', '[20-30)', '[30-50)', '[50-70)','[70-90)', '[90-120)', ' [120 < )'), rotation=30)
bar1 = plt.bar(np.arange(len(errorRateListOfFast)) + bar_width, errorRateListOfFast, bar_width, align='center', alpha=opacity, color='b', label='Fast <= 6 sec.')
bar2 = plt.bar(range(len(errorRateListOfSlow)), errorRateListOfSlow, bar_width, align='center', alpha=opacity, color='r', label='Slower > 6 sec.')

# Add counts above the two bar graphs
for rect in bar1 + bar2:
    height = rect.get_height()
    plt.text(rect.get_x() + rect.get_width() / 2.0, height, f'{height:.0f}', ha='center', va='bottom')

plt.legend()
plt.tight_layout()
plt.show()

Giving you:

ha='center' and va='bottom' refer to how the text is aligned in relation to the x and y co-ordinates, i.e. horizontal and vertical alignment.