fix python 3.5 compatibility

- move workaround for PEP487 ty secop.lib.py35compat
- add missing context manager to TCPServer
- remove redundant code in secop/property.py

Change-Id: I0822010f196ad6cec5ec44e990013b79c5d4048b
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27090
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>

secop/lib/py35compat.py

@@ -0,0 +1,58 @@
+#  -*- coding: utf-8 -*-
+# *****************************************************************************
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 of the License, or (at your option) any later
+# version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+# details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program; if not, write to the Free Software Foundation, Inc.,
+# 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+#
+# Module authors:
+#   Markus Zolliker <markus.zolliker@psi.ch>
+#
+# *****************************************************************************
+"""workaround for python versions older than 3.6
+
+``Object`` must be inherited for classes needing support for
+__init_subclass__ and __set_name__
+"""
+
+
+if hasattr(object, '__init_subclass__'):
+    class Object:
+        pass
+else:
+    class PEP487Metaclass(type):
+        # support for __set_name__ and __init_subclass__ for older python versions
+        # slightly modified from PEP487 doc
+        def __new__(cls, *args, **kwargs):
+            if len(args) != 3:
+                return super().__new__(cls, *args)
+            name, bases, ns = args
+            init = ns.get('__init_subclass__')
+            if callable(init):
+                ns['__init_subclass__'] = classmethod(init)
+            newtype = super().__new__(cls, name, bases, ns)
+            for k, v in newtype.__dict__.items():
+                func = getattr(v, '__set_name__', None)
+                if func is not None:
+                    func(newtype, k)
+            if bases:
+                super(newtype, newtype).__init_subclass__(**kwargs)  # pylint: disable=bad-super-call
+            return newtype
+
+        def __init__(cls, name, bases, ns, **kwargs):
+            super().__init__(name, bases, ns)
+
+    class Object(metaclass=PEP487Metaclass):
+        @classmethod
+        def __init_subclass__(cls, *args, **kwargs):
+            pass

secop/properties.py

@@ -24,24 +24,12 @@
 
 
 import inspect
-import sys
 
 from secop.errors import BadValueError, ConfigError, ProgrammingError
+from secop.lib.py35compat import Object
 
 
-class HasDescriptorMeta(type):
+class HasDescriptors(Object):
-    def __new__(cls, name, bases, attrs):
-        newtype = type.__new__(cls, name, bases, attrs)
-        if sys.version_info < (3, 6):
-            # support older python versions
-            for key, attr in attrs.items():
-                if hasattr(attr, '__set_name__'):
-                    attr.__set_name__(newtype, key)
-            newtype.__init_subclass__()
-        return newtype
-
-
-class HasDescriptors(metaclass=HasDescriptorMeta):
     @classmethod
     def __init_subclass__(cls):
         # when migrating old style declarations, sometimes the trailing comma is not removed
@@ -142,12 +130,6 @@ class HasProperties(HasDescriptors):
     @classmethod
     def __init_subclass__(cls):
         super().__init_subclass__()
-        # raise an error when an attribute is a tuple with one single descriptor as element
-        # when migrating old style declarations, sometimes the trailing comma is not removed
-        bad = [k for k, v in cls.__dict__.items()
-               if isinstance(v, tuple) and len(v) == 1 and hasattr(v[0], '__set_name__')]
-        if bad:
-            raise ProgrammingError('misplaced trailing comma after %s.%s' % (cls.__name__, '/'.join(bad)))
         properties = {}
         # using cls.__bases__ and base.propertyDict for this would fail on some multiple inheritance cases
         for base in reversed(cls.__mro__):

secop/protocol/interface/tcp.py

@@ -202,3 +202,11 @@ class TCPServer(socketserver.ThreadingTCPServer):
         if ntry:
             self.log.warning('tried again %d times after "Address already in use"' % ntry)
         self.log.info("TCPServer initiated")
+
+    # py35 compatibility
+    if not hasattr(socketserver.ThreadingTCPServer, '__exit__'):
+        def __enter__(self):
+            return self
+
+        def __exit__(self, *args):
+            self.server_close()