Fix updating of formulaic.__version__ during build.

.gitignore

@@ -26,6 +26,7 @@ share/python-wheels/
 .installed.cfg
 *.egg
 MANIFEST
+formulaic/_version.py
 
 # PyInstaller
 #  Usually these files are written by a python script from a template

formulaic/__init__.py

@@ -1,14 +1,23 @@
-from ._version import __author__, __author_email__, __version__
 from .formula import Formula, FormulaSpec
 from .materializers import FactorValues
 from .model_matrix import ModelMatrix, ModelMatrices
 from .model_spec import ModelSpec, ModelSpecs
 from .sugar import model_matrix
 
+try:
+    from ._version import __version__, __version_tuple__
+except ImportError:  # pragma: no cover
+    __version__ = version = "unknown"
+    __version_tuple__ = version_tuple = ("unknown",)
+
+__author__ = "Matthew Wardrop"
+__author_email__ = "[email protected]"
+
 __all__ = [
     "__author__",
     "__author_email__",
     "__version__",
+    "__version_tuple__",
     "Formula",
     "FormulaSpec",
     "ModelMatrix",

pyproject.toml

@@ -49,6 +49,9 @@ calculus = ["sympy<1.10,>=1.3"]
 [tool.hatch.version]
 source = "vcs"
 
+[tool.hatch.build.hooks.vcs]
+version-file = "formulaic/_version.py"
+
 # Build target configuration
 
 [tool.hatch.build.targets.sdist]