ENH: emit warning if SciPy is not installed

pyproject.toml

@@ -50,7 +50,10 @@ name = "ampform"
 requires-python = ">=3.7"
 
 [project.optional-dependencies]
-all = ["ampform[viz]"]
+all = [
+    "ampform[scipy]",
+    "ampform[viz]",
+]
 dev = [
     "ampform[all]",
     "ampform[doc]",
@@ -62,7 +65,7 @@ dev = [
 ]
 doc = [
     "Sphinx >=3",
-    "ampform[viz]",
+    "ampform[all]",
     "black",
     "ipympl",
     "matplotlib",
@@ -102,13 +105,15 @@ mypy = [
     "mypy >=0.730",
     "sphinx-api-relink >=0.0.3",
 ]
+scipy = ["scipy"]
 sty = [
     "ampform[format]",
     "ampform[lint]",
     "ampform[test]", # for pytest type hints
     "pre-commit >=1.4.0",
 ]
 test = [
+    "ampform[scipy]",
     "black",
     "ipywidgets", # symplot
     "nbmake",
@@ -117,7 +122,6 @@ test = [
     "pytest-cov",
     "pytest-profiling",
     "pytest-xdist",
-    "scipy",
 ]
 viz = ["graphviz"]
 
@@ -185,6 +189,10 @@ warn_unused_configs = true
 ignore_missing_imports = true
 module = ["graphviz.*"]
 
+[[tool.mypy.overrides]]
+ignore_missing_imports = true
+module = ["scipy.*"]
+
 [[tool.mypy.overrides]]
 ignore_missing_imports = true
 module = ["ipywidgets.*"]

src/ampform/sympy/__init__.py

@@ -19,6 +19,7 @@
 import os
 import pickle
 import re
+import warnings
 from abc import abstractmethod
 from os.path import abspath, dirname, expanduser
 from textwrap import dedent
@@ -364,6 +365,7 @@ def doit(self, **hints):
         return self.func(*args)
 
     def _numpycode(self, printer, *args):
+        _warn_if_scipy_not_installed()
         integration_vars, limits = _unpack_integral_limits(self)
         if len(limits) != 1 or len(integration_vars) != 1:
             msg = f"Cannot handle {len(limits)}-dimensional integrals"
@@ -383,3 +385,14 @@ def _numpycode(self, printer, *args):
             f" epsabs={self.abs_tolerance}, epsrel={self.abs_tolerance},"
             f" limit={self.limit})[0]"
         )
+
+
+def _warn_if_scipy_not_installed() -> None:
+    try:
+        import scipy  # noqa: F401  # pyright: ignore[reportUnusedImport, reportMissingImports]
+    except ImportError:
+        warnings.warn(
+            "Scipy is not installed. Install with 'pip install scipy' or with 'pip"
+            " install ampform[scipy]'",
+            stacklevel=1,
+        )