feat: lazy-load PerthNet without importing librosa

README.md

@@ -24,6 +24,14 @@ Perth enables you to embed imperceptible watermarks in audio files and later det
 pip install resemble-perth
 ```
 
+Core install is `torch` + `torchaudio` only. `librosa` (and `soxr`) pull LGPL
+code and are **not** imported by `perth.perth_net` / `PerthNet`. Install the
+optional extra only if you need the CLI or librosa I/O:
+
+```bash
+pip install 'resemble-perth[audio]'
+```
+
 ### From Source
 
 ```bash

pyproject.toml

@@ -32,14 +32,18 @@ classifiers = [
 
 dependencies = [
     "PyYAML>=6.0",
-    "librosa>=0.11.0",
     "numpy>=1.24.0",
-    "pydub>=0.25.1",
-    "soundfile>=0.12.0",
     "torch>=2.1.0",
     "torchaudio>=2.1.0",
 ]
 
+[project.optional-dependencies]
+audio = [
+    "librosa>=0.11.0",
+    "pydub>=0.25.1",
+    "soundfile>=0.12.0",
+]
+
 [dependency-groups]
 examples = [
     "tqdm>=4.64.0",

src/perth/perth_net/__init__.py

@@ -1,4 +1,15 @@
-from .perth_net_implicit.perth_watermarker import PerthImplicitWatermarker  # noqa: E402, F401
-from ..config import Config
+from perth.config import Config
 
-PREPACKAGED_MODELS_DIR = Config.get_default_models_dir()  # For backward compatibility
+PREPACKAGED_MODELS_DIR = Config.get_default_models_dir()
+
+
+def __getattr__(name: str):
+    """Load the implicit watermarker only when requested.
+
+    Importing ``perth.perth_net`` or ``PerthNet`` must not pull in librosa/soxr.
+    """
+    if name == "PerthImplicitWatermarker":
+        from .perth_net_implicit.perth_watermarker import PerthImplicitWatermarker
+
+        return PerthImplicitWatermarker
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

src/perth/perth_net/perth_net_implicit/perth_watermarker.py

@@ -1,6 +1,5 @@
 import torch
 import numpy as np
-from librosa import resample
 
 from .model.perth_net import PerthNet
 from perth.watermarker import WatermarkerBase
@@ -12,6 +11,35 @@ def _to_tensor(x, device):
     return x.to(dtype=torch.float, device=device)
 
 
+def _resample(signal, orig_sr, target_sr, *, res_type=None):
+    """Resample with torchaudio; librosa is an optional extra, not a core dep."""
+    try:
+        from torchaudio.functional import resample as torchaudio_resample
+
+        tensor = signal if isinstance(signal, torch.Tensor) else torch.as_tensor(signal)
+        was_numpy = not isinstance(signal, torch.Tensor)
+        if tensor.ndim == 1:
+            tensor = tensor.unsqueeze(0)
+            squeezed = True
+        else:
+            squeezed = False
+        out = torchaudio_resample(tensor.float(), orig_sr, target_sr)
+        if squeezed:
+            out = out.squeeze(0)
+        return out.numpy() if was_numpy else out
+    except Exception:
+        try:
+            from librosa import resample
+        except ImportError as error:
+            raise ImportError(
+                "PerthNet resample fell back to librosa, but librosa is not installed. "
+                "Install resemble-perth[audio] or keep torchaudio available."
+            ) from error
+
+        kwargs = {} if res_type is None else {"res_type": res_type}
+        return resample(signal, orig_sr=orig_sr, target_sr=target_sr, **kwargs)
+
+
 class PerthImplicitWatermarker(WatermarkerBase):
     def __init__(
         self,
@@ -33,7 +61,7 @@ def __init__(
     def apply_watermark(self, signal, sample_rate, **_):
         change_rate = sample_rate != self.perth_net.hp.sample_rate
         signal = (
-            resample(
+            _resample(
                 signal, orig_sr=sample_rate, target_sr=self.perth_net.hp.sample_rate
             )
             if change_rate
@@ -53,7 +81,7 @@ def apply_watermark(self, signal, sample_rate, **_):
         wm_signal = self.perth_net.ap.magphase_to_signal(wm_magspec, phase)
         wm_signal = wm_signal.detach().cpu().numpy()
         return (
-            resample(
+            _resample(
                 wm_signal, orig_sr=self.perth_net.hp.sample_rate, target_sr=sample_rate
             )
             if change_rate
@@ -63,7 +91,7 @@ def apply_watermark(self, signal, sample_rate, **_):
     def get_watermark(self, wm_signal, sample_rate, round=True, **_):
         change_rate = sample_rate != self.perth_net.hp.sample_rate
         if change_rate:
-            wm_signal = resample(
+            wm_signal = _resample(
                 wm_signal,
                 orig_sr=sample_rate,
                 target_sr=self.perth_net.hp.sample_rate,

tests/test_lazy_perth_net.py

@@ -0,0 +1,41 @@
+import subprocess
+import sys
+import unittest
+
+
+class TestLazyPerthNetImports(unittest.TestCase):
+    def test_import_perth_net_without_librosa(self):
+        code = (
+            "import sys\n"
+            "from perth.perth_net.perth_net_implicit.model.perth_net import PerthNet\n"
+            "assert PerthNet is not None\n"
+            "assert 'librosa' not in sys.modules, sys.modules.keys()\n"
+            "assert 'soxr' not in sys.modules\n"
+        )
+        result = subprocess.run(
+            [sys.executable, "-c", code],
+            capture_output=True,
+            text=True,
+        )
+        self.assertEqual(result.returncode, 0, result.stderr)
+
+    def test_perth_package_import_without_librosa(self):
+        code = (
+            "import sys\n"
+            "import perth\n"
+            "assert 'librosa' not in sys.modules, sys.modules.keys()\n"
+        )
+        result = subprocess.run(
+            [sys.executable, "-c", code],
+            capture_output=True,
+            text=True,
+        )
+        self.assertEqual(result.returncode, 0, result.stderr)
+
+    def test_core_dependencies_do_not_declare_librosa(self):
+        from pathlib import Path
+
+        text = Path(__file__).resolve().parents[1].joinpath("pyproject.toml").read_text()
+        core = text.split("[project.optional-dependencies]", 1)[0]
+        self.assertNotIn("librosa", core)
+        self.assertIn("librosa>=0.11.0", text)