from __future__ import absolute_import, division, print_function

import sys

import types

PY2 = sys.version_info[0] == 2

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()

    def iterkeys(d):

        return d.iterkeys()

    # 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 iterkeys(d):

        return d.keys()

    def metadata_proxy(d):

        return types.MappingProxyType(dict(d))