Pin cython<3

Signed-off-by: Keith Battocchi <kebatt@microsoft.com>

.github/workflows/publish-documentation.yml

@@ -63,7 +63,7 @@ jobs:
           python-version: 3.8 # because of our supported TensorFlow versions, must build on 3.6-3.8
       - run: python -m pip install --upgrade pip && pip install --upgrade setuptools
         name: Ensure latest pip and setuptools
-      - run: pip install -U cython && pip install -e .[all] ${{ inputs.use_lkg && '-r lkg.txt' }}
+      - run: pip install -e .[all] ${{ inputs.use_lkg && '-r lkg.txt' }}
         name: Install econml[all]
       - run: sudo apt-get -yq install graphviz
         name: Install graphviz

.github/workflows/publish-package.yml

@@ -91,7 +91,7 @@ jobs:
           python-version: 3.8 # because of our supported TensorFlow versions, must build on 3.6-3.8
       - run: python -m pip install --upgrade pip && pip install --upgrade setuptools
         name: Ensure latest pip and setuptools
-      - run: pip install -U cython && pip install -e .[all] ${{ inputs.use_lkg && '-r lkg.txt' }}
+      - run: pip install -e .[all] ${{ inputs.use_lkg && '-r lkg.txt' }}
         name: Install econml[all]
       - run: python setup.py sdist
         name: Build sdist

pyproject.toml

@@ -4,7 +4,7 @@ requires = [
     "wheel",
     "oldest-supported-numpy",
     "scipy",
-    "cython"
+    "cython<3" # Our native code has several incompatibilities with Cython 3
 ]
 build-backend = "setuptools.build_meta"