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Preserve Matplotlib backend across sys_info() #13963

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Merged
larsoner merged 3 commits into from
Jun 15, 2026
Merged

Preserve Matplotlib backend across sys_info() #13963

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d9d6144
Preserve Matplotlib backend across sys_info()
Jun 14, 2026
d74e388
Add changelog entry for sys_info backend fix
sappelhoff Jun 15, 2026
6b42b07
Merge branch 'main' into fix/sys_info-backend-side-effect
larsoner Jun 15, 2026
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1 change: 1 addition & 0 deletions doc/changes/dev/13963.bugfix.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fixed bug where :func:`mne.sys_info` would silently change the active Matplotlib backend (e.g. when ``ipympl`` is installed) as an import-time side effect, by `Stefan Appelhoff`_.
18 changes: 18 additions & 0 deletions mne/utils/config.py
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Original file line number Diff line number Diff line change
Expand Up @@ -880,6 +880,15 @@ def sys_info(
unicode = False
mne_version_good = True
import_names = dict(hedtools="hed")
# ``import_module`` below imports each optional dependency purely to read its
# version. Some packages change global state at import time -- most notably
# ``ipympl``, which switches the Matplotlib backend. Snapshot the backend so
# that merely calling ``sys_info`` does not mutate the caller's backend.
mpl_backend = None
with contextlib.suppress(Exception):
import matplotlib

mpl_backend = matplotlib.get_backend()
for mi, mod_name in enumerate(use_mod_names):
# upcoming break
if mod_name == "": # break
Expand Down Expand Up @@ -955,6 +964,15 @@ def sys_info(
out(f"\n{pre}{' ' * ljust}{op.dirname(mod.__file__)}")
out("\n")

# Restore the Matplotlib backend in case importing a dependency above
# (e.g. ipympl) changed it as an import-time side effect.
if mpl_backend is not None:
with contextlib.suppress(Exception):
import matplotlib

if matplotlib.get_backend() != mpl_backend:
matplotlib.use(mpl_backend, force=True)

if not mne_version_good:
out(
"\nTo update to the latest supported release version to get bugfixes and "
Expand Down
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