Is the intended consequence of this PR that

plt.xkcd()
plt.figure()
plt.plot(...)

is not working any more as in this example and that instead you have to use it as a context?

with plt.xkcd():
    plt.figure()
    plt.plot(...)

The latter is shown in this example.

Would it be possible to issue a warning if a function is used without a context?

No, that was not the intent and is a bug.
Sigh, circular references and garbage collection...

Basically, right now we have a test that the requested pattern works:

def test_xkcd_no_cm():
    assert mpl.rcParams["path.sketch"] is None
    plt.xkcd()
    assert mpl.rcParams["path.sketch"] == (1, 100, 2)

but that's only because the cyclic gc (usually) doesn't trigger just before the second assert; as:

from pylab import *
import gc
print(rcParams["path.sketch"])
plt.xkcd()
gc.collect()
print(rcParams["path.sketch"])
plt.show()

always gives None, None.

Bigger picture: Is the xkcd style/function/context manager really something that we want to continue supporting?

I don't have any problems with it sticking around, although switching to pythonic styles (per the "Python-syntax matplotlibrc" PR) would make this infinitely easier (would become a regular style).

I'd work on pythonic styles first, rather than trying to get this to work again.

As I see it the xkcd function shows the power of the library. It's kind of an advertisement of what is possible with matplotlib. So yes, I'm totally in favour of keeping that (although I don't care if it's a pyplot function or a style or usable only with contexts etc.).

Or maybe just because it's great fun. 😎

@anntzer Well, as you know (#6157), there is a challenge about converting plt.xkcd into a “regular” style by mean of an rcparams-file because it uses a patheffect rcparams, which cannot be parsed at the moment :/.

We discussed the pythonic-mplrc proposal during this week's dev call (btw you should join, it's fun :-)) and looks like we'll make some progress on that.

Glad to hear that things are moving :) (did not read the notes from this week's call yet 🐑 )