How do you add a shaded area between two points in a matplotlib plot?

In the example matplotlib plot below, I manually added the shaded, yellow area using Skitch. I'd like to know how to do this sans-Skitch.

You can just use the function `axvspan`

. The advantage to this is that the vertical region (or horizontal, in the case of `axhspan`

) will remain shaded regardless of how you pan/zoom the plot. There's a complete example here.

See a simple example below:

```
import numpy as np
import matplotlib.pyplot as plt
x = np.linspace(0, 20, 500)
y = np.cos(3*x) - 2*np.cos(5*x) + 0.5*np.cos(6*x)
a = 5
b = 15
plt.axvspan(a, b, color='y', alpha=0.5, lw=0)
plt.plot(x, y)
plt.savefig('shade.png', dpi=300)
plt.show()
```

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