Shade the area between two axhline using matplotlib

Question

What I'm trying to achieve: a plot with two axhline horizontal lines, with the area between them shaded.

The best so far:

    ax.hline(y1, color=c)
    ax.hline(y2, color=c)
    ax.fill_between(ax.get_xlim(), y1, y2, color=c, alpha=0.5)

The problem is that this leaves a small amount of blank space to the left and right of the shaded area.

I understand that this is likely due to the plot creating a margin around the used/data area of the plot. So, how do I get the fill_between to actually cover the entire plot without matplotlib rescaling the x-axis after drawing? Is there an alternative to get_xlim that would give me appropriate limits of the plot, or an alternative to fill_between?

This is the current result:

Note that this is part of a larger grid layout with several plots, but they all leave a similar margin around these shaded areas.

Answer 1

Not strictly speaking an answer to the question of getting the outer limits, but it does solve the problem. Instead of using fill_between, I should have used:

    ax.axhspan(y1, y2, facecolor=c, alpha=0.5)

Result:

Answer 2

ax.get_xlim() does return the limits of the axis, not that of the data:

Axes.get_xlim()

Returns the current x-axis limits as the tuple (left, right).

But Matplotlib simply rescales the x-axis after drawing the fill_between:

import matplotlib.pylab as pl
import numpy as np

pl.figure()
ax=pl.subplot(111)
pl.plot(np.random.random(10))

print(ax.get_xlim())

pl.fill_between(ax.get_xlim(), 0.5, 1)

print(ax.get_xlim())

This results in:

(-0.45000000000000001, 9.4499999999999993)

(-0.94499999999999995, 9.9449999999999985)

If you don't want to manually set the x-limits, you could use something like:

import matplotlib.pylab as pl
import numpy as np

pl.figure()
ax=pl.subplot(111)
pl.plot(np.random.random(10))

xlim = ax.get_xlim()

pl.fill_between(xlim, 0.5, 1)

ax.set_xlim(xlim)