_compat.py

""" Compatibility layer.

    Some py2/py3 compatibility support based on a stripped down
    version of six so we don't have to depend on a specific version
    of it.

    :copyright: (c) 2014 by Armin Ronacher.
    :license: BSD
"""
import sys

PY2 = sys.version_info[0] == 2
_identity = lambda x: x


if not PY2:
    text_type = str
    string_types = (str,)
    integer_types = (int, )

    iterkeys = lambda d: iter(d.keys())
    itervalues = lambda d: iter(d.values())
    iteritems = lambda d: iter(d.items())

    from io import StringIO

    def reraise(tp, value, tb=None):
        if value.__traceback__ is not tb:
            raise value.with_traceback(tb)
        raise value

    implements_to_string = _identity

else:
    text_type = unicode
    string_types = (str, unicode)
    integer_types = (int, long)

    iterkeys = lambda d: d.iterkeys()
    itervalues = lambda d: d.itervalues()
    iteritems = lambda d: d.iteritems()

    from cStringIO import StringIO

    exec('def reraise(tp, value, tb=None):\n raise tp, value, tb')

    def implements_to_string(cls):
        cls.__unicode__ = cls.__str__
        cls.__str__ = lambda x: x.__unicode__().encode('utf-8')
        return cls


def with_metaclass(meta, *bases):
    # This requires a bit of explanation: the basic idea is to make a
    # dummy metaclass for one level of class instantiation that replaces
    # itself with the actual metaclass.  Because of internal type checks
    # we also need to make sure that we downgrade the custom metaclass
    # for one level to something closer to type (that's why __call__ and
    # __init__ comes back from type etc.).
    #
    # This has the advantage over six.with_metaclass in that it does not
    # introduce dummy classes into the final MRO.
    class metaclass(meta):
        __call__ = type.__call__
        __init__ = type.__init__
        def __new__(cls, name, this_bases, d):
            if this_bases is None:
                return type.__new__(cls, name, (), d)
            return meta(name, bases, d)
    return metaclass('temporary_class', None, {})


# Certain versions of pypy have a bug where clearing the exception stack
# breaks the __exit__ function in a very peculiar way.  This is currently
# true for pypy 2.2.1 for instance.  The second level of exception blocks
# is necessary because pypy seems to forget to check if an exception
# happend until the next bytecode instruction?
BROKEN_PYPY_CTXMGR_EXIT = False
if hasattr(sys, 'pypy_version_info'):
    class _Mgr(object):
        def __enter__(self):
            return self
        def __exit__(self, *args):
            sys.exc_clear()
    try:
        try:
            with _Mgr():
                raise AssertionError()
        except:
            raise
    except TypeError:
        BROKEN_PYPY_CTXMGR_EXIT = True
    except AssertionError:
        pass

try:
    from collections import OrderedDict
except ImportError:
    from UserDict import DictMixin

    class OrderedDict(dict, DictMixin):

        null = object()

        def __init__(self, *args, **kwargs):
            self.clear()
            self.update(*args, **kwargs)

        def clear(self):
            self.__map = dict()
            self.__order = list()
            dict.clear(self)

    def __setitem__(self, key, value):
        if key not in self:
            self.__map[key] = len(self.__order)
            self.__order.append(key)
        dict.__setitem__(self, key, value)

    def __delitem__(self, key):
        dict.__delitem__(self, key)
        self.__map.pop(key)
        self.__order = self.null

    def __iter__(self):
        for key in self.__order:
            if key is not self.null:
                yield key

    def keys(self):
        return list(self)

    setdefault = DictMixin.setdefault
    update = DictMixin.update
    pop = DictMixin.pop
    values = DictMixin.values
    items = DictMixin.items
    iterkeys = DictMixin.iterkeys
    itervalues = DictMixin.itervalues
    iteritems = DictMixin.iteritems

try:
    from importlib import import_module
except ImportError:

    def _resolve_name(name, package, level):
        """Return the absolute name of the module to be imported."""
        if not hasattr(package, 'rindex'):
            raise ValueError("'package' not set to a string")
        dot = len(package)
        for x in xrange(level, 1, -1):
            try:
                dot = package.rindex('.', 0, dot)
            except ValueError:
                raise ValueError("attempted relative import beyond top-level "
                                "package")
        return "%s.%s" % (package[:dot], name)

    def import_module(name, package=None):
        """Import a module.

        The 'package' argument is required when performing a relative import. It
        specifies the package to use as the anchor point from which to resolve the
        relative import to an absolute import.

        """
        if name.startswith('.'):
            if not package:
                raise TypeError("relative imports require the 'package' argument")
            level = 0
            for character in name:
                if character != '.':
                    break
                level += 1
            name = _resolve_name(name[level:], package, level)
        __import__(name)
        return sys.modules[name]