[Python] Matplotlib polar bar chart - donut hole in middle

I have the following chart and code:

Code:

def generate_chart_capability(student, df):
# canvas sizing
plt.figure(figsize=(10, 10))
# plot polar axis
ax = plt.subplot(111, polar=True, projection='polar')
ax.set_theta_direction(-1)
ax.set_theta_offset(np.pi / 1.6)
ax.set_xticklabels([])
ax.set_yticklabels([1, 2, 3, 4, 5], size=21)

# Compute the width of each bar. In total, we have 2*Pi = 360°
width = 2 * np.pi / len(df.index)
# Compute the angle each bar is centered on:
indexes = list(range(1, len(df.index) + 1))
angles = [element * width for element in indexes]
# Compute the heights
heights = df.Value
# Colour the bars
c = ['#054998', '#3660B3', '#5579CF', '#7392EB', '#90ADFF', '#ADC8FF']

# Draw the bars
ax.bar(x=angles, height=heights, width=width, color=c, bottom=0, linewidth=2, edgecolor="white")
ax.set_ylim([0, 5])

# Save the figure
plt.savefig('app/static/output/capability_chart_' + student + '.png')

# Close the figure
plt.clf()


Chart:



I would like to have a donut hole in the middle of the chart (basically unfilled) between 0 and 1 as this range of values does not occur in my data.

I have tried to set bottom=1 in ax.bar but that just adds 1 to the data values.

How can I achieve this unfilled first region?

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