Set c_api_binop_methods compiler directive to True

This retains Cython 0.x behavior for arithmetic operators for
Cython >= 3.0.0.

Author: spencerkclark

Changelog

@@ -2,6 +2,8 @@ since version 1.6.2 release
 ===========================
  * add support for formats without separators in strptime (e.g. '20200229', issue #301).
    This required removing support for > 4 digit years.
+ * set the c_api_binop_methods compiler directive to True to retain Cython 0.x
+   behavior for arithmetic operators for Cython >= 3.0.0 (issue #271).
 
 version 1.6.2 (release tag v1.6.2rel)
 =====================================

pyproject.toml

@@ -1,3 +1,3 @@
 [build-system]
-requires = ["setuptools>=41.2", "cython", "wheel", "oldest-supported-numpy"]
+requires = ["setuptools>=41.2", "cython>=0.29.20", "wheel", "oldest-supported-numpy"]
 build-backend = "setuptools.build_meta"

requirements-dev.txt

@@ -1,7 +1,7 @@
 check-manifest
 coverage
 coveralls
-cython>0.26.1
+cython>=0.29.20
 pytest
 pytest-cov
 sphinx

setup.py

@@ -16,7 +16,14 @@
 BASEDIR = os.path.abspath(os.path.dirname(__file__))
 SRCDIR = os.path.join(BASEDIR,'src')
 CMDS_NOCYTHONIZE = ['clean','clean_cython','sdist']
-COMPILER_DIRECTIVES = {}
+COMPILER_DIRECTIVES = {
+    # Cython 3.0.0 changes the default of the c_api_binop_methods directive to
+    # False, resulting in errors in datetime and timedelta arithmetic:
+    # https://github.com/Unidata/cftime/issues/271.  We explicitly set it to
+    # True to retain Cython 0.x behavior for future Cython versions.  This
+    # directive was added in Cython version 0.29.20.
+    "c_api_binop_methods": True
+}
 DEFINE_MACROS = [("NPY_NO_DEPRECATED_API", "NPY_1_7_API_VERSION")] 
 FLAG_COVERAGE = '--cython-coverage'  # custom flag enabling Cython line tracing
 NAME = 'cftime'