Changed fill.py example to be less misleading

[samvaughan]

PR Summary

I've changed /examples/lines_bars_and_markers/fill.py to be less misleading, following issues #5827 and #7956.

These plots were over-simplified because fill was acting just like fill_between, since the final line of the region to be filled was completely along the x-axis. I've changed the first example to be a simple polygon (as suggested in #5827) and the second to not have the final point at y=0 anymore. I've also outlined the region being filled, to make what's going on more obvious.

PR Checklist

• Has Pytest style unit tests
• Code is PEP 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

[timhoffm]

Thanks for the update.

https://8797-1385122-gh.circle-artifacts.com/0/home/circleci/project/doc/build/html/gallery/lines_bars_and_markers/fill.html?highlight=fill

I don't find the polygon particularly instructive:

• Start and endpoint are still at the same y.
• I think we could leave out the grid and thus the zorder.

maybe simply

x = [0, 1, 3, 1]
y = [1, 2, 1, 0]

fig, ax = plt.subplots()
ax.fill(x, y)

Minor things:

• Single blank lines in the code example are sufficient. No need for two blank lines.
• For completeness, the first plot should get a plt.plot() as well.

[samvaughan]

Sure, no problem. I've removed the grid and made the first example a square

x = [0, 1, 2, 1]
y = [1, 2, 1, 0]
 
fig, ax = plt.subplots()
ax.fill(x, y)

and outlined it in black with plt.plot(). I've removed the double spaces too.

[timhoffm]

Sorry, I didn't mean plt.plot() but plt.show(). My bad. The outline does not add extra information in this first example. It's sufficient to illustrate this in the second example.

[samvaughan]

No worries, just changed it!

[timhoffm]

Looks good

https://circleci.com/gh/matplotlib/matplotlib/8842/artifacts/0//home/circleci/project/doc/build/html/index.html