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Backport PR #29721 on branch v3.10.x (FIX: pyplot auto-backend detection case-sensitivity fixup) #29754

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Merged
merged 1 commit into from
Mar 21, 2025
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Merged

Backport PR #29721 on branch v3.10.x (FIX: pyplot auto-backend detection case-sensitivity fixup) #29754

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15 changes: 9 additions & 6 deletions lib/matplotlib/pyplot.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2715,12 +2715,15 @@ def polar(*args, **kwargs) -> list[Line2D]:
# If rcParams['backend_fallback'] is true, and an interactive backend is
# requested, ignore rcParams['backend'] and force selection of a backend that
# is compatible with the current running interactive framework.
if (rcParams["backend_fallback"]
and rcParams._get_backend_or_none() in ( # type: ignore[attr-defined]
set(backend_registry.list_builtin(BackendFilter.INTERACTIVE)) -
{'webagg', 'nbagg'})
and cbook._get_running_interactive_framework()):
rcParams._set("backend", rcsetup._auto_backend_sentinel)
if rcParams["backend_fallback"]:
requested_backend = rcParams._get_backend_or_none() # type: ignore[attr-defined]
requested_backend = None if requested_backend is None else requested_backend.lower()
available_backends = backend_registry.list_builtin(BackendFilter.INTERACTIVE)
if (
requested_backend in (set(available_backends) - {'webagg', 'nbagg'})
and cbook._get_running_interactive_framework()
):
rcParams._set("backend", rcsetup._auto_backend_sentinel)

# fmt: on

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25 changes: 24 additions & 1 deletion lib/matplotlib/tests/test_rcparams.py
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Original file line number Diff line number Diff line change
Expand Up @@ -521,10 +521,11 @@ def test_rcparams_reset_after_fail():


@pytest.mark.skipif(sys.platform != "linux", reason="Linux only")
def test_backend_fallback_headless(tmp_path):
def test_backend_fallback_headless_invalid_backend(tmp_path):
env = {**os.environ,
"DISPLAY": "", "WAYLAND_DISPLAY": "",
"MPLBACKEND": "", "MPLCONFIGDIR": str(tmp_path)}
# plotting should fail with the tkagg backend selected in a headless environment
with pytest.raises(subprocess.CalledProcessError):
subprocess_run_for_testing(
[sys.executable, "-c",
Expand All @@ -536,6 +537,28 @@ def test_backend_fallback_headless(tmp_path):
env=env, check=True, stderr=subprocess.DEVNULL)


@pytest.mark.skipif(sys.platform != "linux", reason="Linux only")
def test_backend_fallback_headless_auto_backend(tmp_path):
# specify a headless mpl environment, but request a graphical (tk) backend
env = {**os.environ,
"DISPLAY": "", "WAYLAND_DISPLAY": "",
"MPLBACKEND": "TkAgg", "MPLCONFIGDIR": str(tmp_path)}

# allow fallback to an available interactive backend explicitly in configuration
rc_path = tmp_path / "matplotlibrc"
rc_path.write_text("backend_fallback: true")

# plotting should succeed, by falling back to use the generic agg backend
backend = subprocess_run_for_testing(
[sys.executable, "-c",
"import matplotlib.pyplot;"
"matplotlib.pyplot.plot(42);"
"print(matplotlib.get_backend());"
],
env=env, text=True, check=True, capture_output=True).stdout
assert backend.strip().lower() == "agg"


@pytest.mark.skipif(
sys.platform == "linux" and not _c_internal_utils.xdisplay_is_valid(),
reason="headless")
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