python matplotlib bar width is not controllable

Question

I have a bar chart drawn using python's matplotlib:

import matplotlib.pyplot as plt
unique=[200]
index = [0]
counts = [7]
alpha=0.4
bar_width=0.1
color='b'
plt.bar(index, counts, bar_width, alpha=alpha, color=color)
# set x and y labels
plt.xlabel('Status')
plt.ylabel('Counts')
# set title and plot
plt.title('Status Counts')
plt.xticks(index + bar_width/2, unique)
plt.show()

Everytime when there is only one bar is drawn, it fills up half of the chart as shown below:

How to fix this? I tried varying the bar_width with no luck.

Answer 1

It doesn't work because you are only giving it one datapoint, so the width really doesn't matter, since it shows the whole bar plus some small space around it, no matter what you set the width to. For a minimal example I left out the incidentals.

Compare the following two examples to see that the bar-width does work:

import matplotlib.pyplot as plt
index = [0,1,2,3,4,5,6]
counts = [7,7,19,2,3,0,1]

bar_width=0.1 
plt.bar(index, counts, bar_width )
plt.show()

vs.

import matplotlib.pyplot as plt
index = [0 ]
counts = [7 ]

bar_width=0.1  
plt.bar(index, counts, bar_width )
plt.show()