1 files changed, 163 insertions, 0 deletions
diff --git a/python/attr/_compat.py b/python/attr/_compat.py
new file mode 100644
index 0000000..5bb0659
--- /dev/null
+++ b/python/attr/_compat.py
@@ -0,0 +1,163 @@
+from __future__ import absolute_import, division, print_function
+
+import platform
+import sys
+import types
+import warnings
+
+
+PY2 = sys.version_info[0] == 2
+PYPY = platform.python_implementation() == "PyPy"
+
+
+if PYPY or sys.version_info[:2] >= (3, 6):
+    ordered_dict = dict
+else:
+    from collections import OrderedDict
+
+    ordered_dict = OrderedDict
+
+
+if PY2:
+    from UserDict import IterableUserDict
+
+    # We 'bundle' isclass instead of using inspect as importing inspect is
+    # fairly expensive (order of 10-15 ms for a modern machine in 2016)
+    def isclass(klass):
+        return isinstance(klass, (type, types.ClassType))
+
+    # TYPE is used in exceptions, repr(int) is different on Python 2 and 3.
+    TYPE = "type"
+
+    def iteritems(d):
+        return d.iteritems()
+
+    # Python 2 is bereft of a read-only dict proxy, so we make one!
+    class ReadOnlyDict(IterableUserDict):
+        """
+        Best-effort read-only dict wrapper.
+        """
+
+        def __setitem__(self, key, val):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise TypeError(
+                "'mappingproxy' object does not support item assignment"
+            )
+
+        def update(self, _):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'update'"
+            )
+
+        def __delitem__(self, _):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise TypeError(
+                "'mappingproxy' object does not support item deletion"
+            )
+
+        def clear(self):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'clear'"
+            )
+
+        def pop(self, key, default=None):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'pop'"
+            )
+
+        def popitem(self):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'popitem'"
+            )
+
+        def setdefault(self, key, default=None):
+            # We gently pretend we're a Python 3 mappingproxy.
+            raise AttributeError(
+                "'mappingproxy' object has no attribute 'setdefault'"
+            )
+
+        def __repr__(self):
+            # Override to be identical to the Python 3 version.
+            return "mappingproxy(" + repr(self.data) + ")"
+
+    def metadata_proxy(d):
+        res = ReadOnlyDict()
+        res.data.update(d)  # We blocked update, so we have to do it like this.
+        return res
+
+
+else:
+
+    def isclass(klass):
+        return isinstance(klass, type)
+
+    TYPE = "class"
+
+    def iteritems(d):
+        return d.items()
+
+    def metadata_proxy(d):
+        return types.MappingProxyType(dict(d))
+
+
+def import_ctypes():
+    """
+    Moved into a function for testability.
+    """
+    import ctypes
+
+    return ctypes
+
+
+if not PY2:
+
+    def just_warn(*args, **kw):
+        """
+        We only warn on Python 3 because we are not aware of any concrete
+        consequences of not setting the cell on Python 2.
+        """
+        warnings.warn(
+            "Missing ctypes.  Some features like bare super() or accessing "
+            "__class__ will not work with slots classes.",
+            RuntimeWarning,
+            stacklevel=2,
+        )
+
+
+else:
+
+    def just_warn(*args, **kw):  # pragma: nocover
+        """
+        We only warn on Python 3 because we are not aware of any concrete
+        consequences of not setting the cell on Python 2.
+        """
+
+
+def make_set_closure_cell():
+    """
+    Moved into a function for testability.
+    """
+    if PYPY:  # pragma: no cover
+
+        def set_closure_cell(cell, value):
+            cell.__setstate__((value,))
+
+    else:
+        try:
+            ctypes = import_ctypes()
+
+            set_closure_cell = ctypes.pythonapi.PyCell_Set
+            set_closure_cell.argtypes = (ctypes.py_object, ctypes.py_object)
+            set_closure_cell.restype = ctypes.c_int
+        except Exception:
+            # We try best effort to set the cell, but sometimes it's not
+            # possible.  For example on Jython or on GAE.
+            set_closure_cell = just_warn
+    return set_closure_cell
+
+
+set_closure_cell = make_set_closure_cell()