Limit deployment target

Author: wjsi

setup.py

@@ -1,8 +1,31 @@
 import os
+import platform
 import sys
 import subprocess
+from sysconfig import get_config_vars
+
+from pkg_resources import parse_version
 from setuptools import setup, find_packages, Extension
 
+# From https://github.com/pandas-dev/pandas/pull/24274:
+# For mac, ensure extensions are built for macos 10.9 when compiling on a
+# 10.9 system or above, overriding distuitls behaviour which is to target
+# the version that python was built for. This may be overridden by setting
+# MACOSX_DEPLOYMENT_TARGET before calling setup.py
+if sys.platform == "darwin":
+    if "MACOSX_DEPLOYMENT_TARGET" not in os.environ:
+        current_system = platform.mac_ver()[0]
+        python_target = get_config_vars().get(
+            "MACOSX_DEPLOYMENT_TARGET", current_system
+        )
+        target_macos_version = "10.9"
+
+        parsed_python_target = parse_version(python_target)
+        parsed_current_system = parse_version(current_system)
+        parsed_macos_version = parse_version(target_macos_version)
+        if parsed_python_target <= parsed_macos_version <= parsed_current_system:
+            os.environ["MACOSX_DEPLOYMENT_TARGET"] = target_macos_version
+
 if sys.version_info[:2] == (3, 6):
     clinic_file = "tools/py36_clinic.py"
 elif sys.version_info[:2] == (3, 7):