Fix python<3.7 on windows

Author: davidbrochart

README.md

@@ -14,13 +14,7 @@ To install the latest release locally, make sure you have
 
     $ pip install jupyter_server
 
-Jupyter Server currently supports the following Python versions:
-
-Platform | Python
---- | ---
-Linux | >=3.5
-OSX | >=3.5
-Windows | >=3.7
+Jupyter Server currently supports Python>=3.5 on Linux, OSX and Windows.
 
 ### Versioning and Branches
 

jupyter_server/__init__.py

@@ -1,6 +1,8 @@
 """The Jupyter Server"""
 
 import os
+import sys
+import subprocess
 
 DEFAULT_STATIC_FILES_PATH = os.path.join(os.path.dirname(__file__), "static")
 DEFAULT_TEMPLATE_PATH_LIST = [
@@ -11,3 +13,16 @@
 del os
 
 from ._version import version_info, __version__
+
+
+def _cleanup():
+    pass
+
+
+# patch subprocess on Windows for python<3.7
+# see https://bugs.python.org/issue37380
+# the fix for python3.7: https://github.com/python/cpython/pull/15706/files
+if sys.platform == 'win32':
+    if sys.version_info < (3, 7):
+        subprocess._cleanup = _cleanup
+        subprocess._active = None