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fix: do not force matplotlib Agg backend on import #53

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Merged
jmrplens merged 4 commits into from
May 30, 2026
Merged

fix: do not force matplotlib Agg backend on import #53

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0930968
fix: do not force matplotlib Agg backend on import
jmrplens May 30, 2026
956ab2c
chore: bump version to 1.2.3
jmrplens May 30, 2026
424cd9d
test: harden backend test with PYTHONPATH and timeout
jmrplens May 30, 2026
cba69d3
test: select Agg backend for the headless test suite
jmrplens May 30, 2026
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4 changes: 0 additions & 4 deletions src/pyoctaveband/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,6 @@

from typing import List, Tuple, overload, Literal

import matplotlib
import numpy as np

from .calibration import calculate_sensitivity
Expand All @@ -17,9 +16,6 @@
from .parametric_filters import WeightingFilter, linkwitz_riley, time_weighting, weighting_filter
from ._version import __version__

# Use non-interactive backend for plots
matplotlib.use("Agg")

# Public methods
__all__ = [
"__version__",
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2 changes: 1 addition & 1 deletion src/pyoctaveband/_version.py
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@@ -1 +1 @@
__version__ = "1.2.2"
__version__ = "1.2.3"
7 changes: 7 additions & 0 deletions tests/conftest.py
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Expand Up @@ -2,6 +2,13 @@
import os
import pytest

# Select a non-interactive matplotlib backend for the headless test suite.
# The library no longer forces a backend (see issue #52), so the test harness
# must opt into Agg itself; otherwise matplotlib picks a GUI backend (e.g.
# TkAgg on Windows runners) and figure creation fails without a display/Tcl.
# Set at import time so it takes effect before any test module imports pyplot.
os.environ.setdefault("MPLBACKEND", "Agg")

def pytest_configure(config):
"""
Configure environment variables for the test session.
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38 changes: 38 additions & 0 deletions tests/test_matplotlib_backend.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,38 @@
# Copyright (c) 2026. Jose M. Requena-Plens

"""
Tests ensuring the package does not hijack the global matplotlib backend.

Importing pyoctaveband must not force a specific (e.g. non-interactive)
backend, so the package can be used during interactive exploration
(IPython, Jupyter). See issue #52.
"""

import os
import subprocess
import sys


def test_import_does_not_override_matplotlib_backend() -> None:
"""Importing pyoctaveband must preserve the user's chosen backend."""
code = (
"import matplotlib\n"
# Pick an explicit, always-available backend the user might have set.
"matplotlib.use('svg')\n"
"before = matplotlib.get_backend()\n"
"import pyoctaveband\n"
"after = matplotlib.get_backend()\n"
"assert before == after, f'backend changed: {before!r} -> {after!r}'\n"
)
# Propagate the parent's sys.path so the subprocess can import the package
# even when it is only on sys.path (e.g. pytest without an installed build).
env = os.environ.copy()
env["PYTHONPATH"] = os.pathsep.join(sys.path)
result = subprocess.run(
[sys.executable, "-c", code],
capture_output=True,
text=True,
env=env,
timeout=30,
)
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assert result.returncode == 0, result.stderr
Comment on lines +12 to +38

@gemini-code-assist gemini-code-assist Bot May 30, 2026

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medium

The subprocess is executed without propagating the current sys.path or setting PYTHONPATH. If the package is not installed in the environment (for example, when running tests locally via pytest where the path is dynamically added to sys.path), the subprocess will fail with ModuleNotFoundError: No module named 'pyoctaveband'.

To ensure the test is robust across different test runners and environments, pass the parent process's sys.path via the PYTHONPATH environment variable to the subprocess.

import os
import subprocess
import sys


def test_import_does_not_override_matplotlib_backend() -> None:
    """Importing pyoctaveband must preserve the user's chosen backend."""
    code = (
        "import matplotlib\n"
        # Pick an explicit, always-available backend the user might have set.
        "matplotlib.use('svg')\n"
        "before = matplotlib.get_backend()\n"
        "import pyoctaveband\n"
        "after = matplotlib.get_backend()\n"
        "assert before == after, f'backend changed: {before!r} -> {after!r}'\n"
    )
    env = os.environ.copy()
    env["PYTHONPATH"] = os.path.pathsep.join(sys.path)
    result = subprocess.run(
        [sys.executable, "-c", code],
        capture_output=True,
        text=True,
        env=env,
    )
    assert result.returncode == 0, result.stderr

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