adapt metaclass usage to Py2/Py3

Cython/Compiler/Nodes.py

@@ -33,6 +33,7 @@ from .StringEncoding import EncodedString, escape_byte_string, split_string_lite
 from . import Future
 from . import Options
 from . import DebugFlags
+from ..Utils import add_metaclass
 
 absolute_path_length = 0
 
@@ -178,15 +179,19 @@ class CheckAnalysers(type):
         return super(CheckAnalysers, cls).__new__(cls, name, bases, attrs)
 
 
+def _with_metaclass(cls):
+    if DebugFlags.debug_trace_code_generation:
+        return add_metaclass(VerboseCodeWriter)(cls)
+    #return add_metaclass(CheckAnalysers)(cls)
+    return cls
+
+
+@_with_metaclass
 class Node(object):
     #  pos         (string, int, int)   Source file position
     #  is_name     boolean              Is a NameNode
     #  is_literal  boolean              Is a ConstNode
 
-    #__metaclass__ = CheckAnalysers
-    if DebugFlags.debug_trace_code_generation:
-        __metaclass__ = VerboseCodeWriter
-
     is_name = 0
     is_none = 0
     is_nonecheck = 0

Cython/Debugger/Tests/test_libcython_in_gdb.py

@@ -5,6 +5,8 @@ Note: debug information is already imported by the file generated by
 Cython.Debugger.Cygdb.make_command_file()
 """
 
+from __future__ import absolute_import
+
 import os
 import re
 import sys
@@ -21,9 +23,10 @@ from test import test_support
 
 import gdb
 
-from Cython.Debugger import libcython
-from Cython.Debugger import libpython
-from Cython.Debugger.Tests import TestLibCython as test_libcython
+from .. import libcython
+from .. import libpython
+from . import TestLibCython as test_libcython
+from ...Utils import add_metaclass
 
 # for some reason sys.argv is missing in gdb
 sys.argv = ['gdb']
@@ -50,14 +53,13 @@ class TraceMethodCallMeta(type):
                 setattr(self, func_name, print_on_call_decorator(func))
 
 
+@add_metaclass(TraceMethodCallMeta)
 class DebugTestCase(unittest.TestCase):
     """
     Base class for test cases. On teardown it kills the inferior and unsets
     all breakpoints.
     """
 
-    __metaclass__ = TraceMethodCallMeta
-
     def __init__(self, name):
         super(DebugTestCase, self).__init__(name)
         self.cy = libcython.cy

Cython/Debugger/libpython.py

@@ -183,6 +183,25 @@ class PrettyPrinterTrackerMeta(type):
         all_pretty_typenames.add(self._typename)
 
 
+# Class decorator that adds a metaclass and recreates the class with it.
+# Copied from 'six'.  See Cython/Utils.py.
+def _add_metaclass(metaclass):
+    """Class decorator for creating a class with a metaclass."""
+    def wrapper(cls):
+        orig_vars = cls.__dict__.copy()
+        slots = orig_vars.get('__slots__')
+        if slots is not None:
+            if isinstance(slots, str):
+                slots = [slots]
+            for slots_var in slots:
+                orig_vars.pop(slots_var)
+        orig_vars.pop('__dict__', None)
+        orig_vars.pop('__weakref__', None)
+        return metaclass(cls.__name__, cls.__bases__, orig_vars)
+    return wrapper
+
+
+@_add_metaclass(PrettyPrinterTrackerMeta)
 class PyObjectPtr(object):
     """
     Class wrapping a gdb.Value that's a either a (PyObject*) within the
@@ -195,8 +214,6 @@ class PyObjectPtr(object):
     to corrupt data, etc; this is the debugger, after all.
     """
 
-    __metaclass__ = PrettyPrinterTrackerMeta
-
     _typename = 'PyObject'
 
     def __init__(self, gdbval, cast_to=None):

Cython/Utils.py

@@ -414,3 +414,20 @@ class LazyStr:
     def __radd__(self, left):
         return left + self.callback()
 
+
+# Class decorator that adds a metaclass and recreates the class with it.
+# Copied from 'six'.
+def add_metaclass(metaclass):
+    """Class decorator for creating a class with a metaclass."""
+    def wrapper(cls):
+        orig_vars = cls.__dict__.copy()
+        slots = orig_vars.get('__slots__')
+        if slots is not None:
+            if isinstance(slots, str):
+                slots = [slots]
+            for slots_var in slots:
+                orig_vars.pop(slots_var)
+        orig_vars.pop('__dict__', None)
+        orig_vars.pop('__weakref__', None)
+        return metaclass(cls.__name__, cls.__bases__, orig_vars)
+    return wrapper