FIX: do not consider webagg and nbagg "interactive" for fallback #15512

Original file line number	Diff line number	Diff line change
Expand Up		@@ -2244,7 +2244,8 @@ def getname_val(identifier):
		# requested, ignore rcParams['backend'] and force selection of a backend that
		# is compatible with the current running interactive framework.
		if (rcParams["backend_fallback"]
	and dict.__getitem__(rcParams, "backend") in _interactive_bk
	and dict.__getitem__(rcParams, "backend") in (
	set(_interactive_bk) - {'WebAgg', 'nbAgg'})
		and cbook._get_running_interactive_framework()):
		dict.__setitem__(rcParams, "backend", rcsetup._auto_backend_sentinel)
		# Set up the backend.
Expand Down

28 changes: 28 additions & 0 deletions lib/matplotlib/tests/test_backend_webagg.py

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Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,28 @@
	import subprocess
	import os
	import sys
	import pytest


	@pytest.mark.parametrize("backend", ["webagg", "nbagg"])
	def test_webagg_fallback(backend):
	if backend == "nbagg":
	pytest.importorskip("IPython")
	env = {}
	if os.name == "nt":
	env = dict(os.environ)
	else:
	env = {"DISPLAY": ""}

	env["MPLBACKEND"] = backend

	test_code = (
	"import os;"
	+ f"assert os.environ['MPLBACKEND'] == '{backend}';"
	+ "import matplotlib.pyplot as plt; "
	+ "print(plt.get_backend());"
	f"assert '{backend}' == plt.get_backend().lower();"
	)
	ret = subprocess.call([sys.executable, "-c", test_code], env=env)

	assert ret == 0

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