_utils.py

from __future__ import absolute_import, division, unicode_literals

import sys
from types import ModuleType

from six import text_type

try:
    import xml.etree.cElementTree as default_etree
except ImportError:
    import xml.etree.ElementTree as default_etree


__all__ = ["default_etree", "MethodDispatcher", "isSurrogatePair",
           "surrogatePairToCodepoint", "moduleFactoryFactory",
           "supports_lone_surrogates", "PY27"]


PY27 = sys.version_info[0] == 2 and sys.version_info[1] >= 7

# Platforms not supporting lone surrogates (\uD800-\uDFFF) should be
# caught by the below test. In general this would be any platform
# using UTF-16 as its encoding of unicode strings, such as
# Jython. This is because UTF-16 itself is based on the use of such
# surrogates, and there is no mechanism to further escape such
# escapes.
try:
    _x = eval('"\\uD800"')  # pylint:disable=eval-used
    if not isinstance(_x, text_type):
        # We need this with u"" because of http://bugs.jython.org/issue2039
        _x = eval('u"\\uD800"')  # pylint:disable=eval-used
        assert isinstance(_x, text_type)
except:  # pylint:disable=bare-except
    supports_lone_surrogates = False
else:
    supports_lone_surrogates = True


class MethodDispatcher(dict):
    """Dict with 2 special properties:

    On initiation, keys that are lists, sets or tuples are converted to
    multiple keys so accessing any one of the items in the original
    list-like object returns the matching value

    md = MethodDispatcher({("foo", "bar"):"baz"})
    md["foo"] == "baz"

    A default value which can be set through the default attribute.
    """

    def __init__(self, items=()):
        # Using _dictEntries instead of directly assigning to self is about
        # twice as fast. Please do careful performance testing before changing
        # anything here.
        _dictEntries = []
        for name, value in items:
            if isinstance(name, (list, tuple, frozenset, set)):
                for item in name:
                    _dictEntries.append((item, value))
            else:
                _dictEntries.append((name, value))
        dict.__init__(self, _dictEntries)
        assert len(self) == len(_dictEntries)
        self.default = None

    def __getitem__(self, key):
        return dict.get(self, key, self.default)


# Some utility functions to deal with weirdness around UCS2 vs UCS4
# python builds

def isSurrogatePair(data):
    return (len(data) == 2 and
            ord(data[0]) >= 0xD800 and ord(data[0]) <= 0xDBFF and
            ord(data[1]) >= 0xDC00 and ord(data[1]) <= 0xDFFF)


def surrogatePairToCodepoint(data):
    char_val = (0x10000 + (ord(data[0]) - 0xD800) * 0x400 +
                (ord(data[1]) - 0xDC00))
    return char_val

# Module Factory Factory (no, this isn't Java, I know)
# Here to stop this being duplicated all over the place.


def moduleFactoryFactory(factory):
    moduleCache = {}

    def moduleFactory(baseModule, *args, **kwargs):
        if isinstance(ModuleType.__name__, type("")):
            name = "_%s_factory" % baseModule.__name__
        else:
            name = b"_%s_factory" % baseModule.__name__

        kwargs_tuple = tuple(kwargs.items())

        try:
            return moduleCache[name][args][kwargs_tuple]
        except KeyError:
            mod = ModuleType(name)
            objs = factory(baseModule, *args, **kwargs)
            mod.__dict__.update(objs)
            if "name" not in moduleCache:
                moduleCache[name] = {}
            if "args" not in moduleCache[name]:
                moduleCache[name][args] = {}
            if "kwargs" not in moduleCache[name][args]:
                moduleCache[name][args][kwargs_tuple] = {}
            moduleCache[name][args][kwargs_tuple] = mod
            return mod

    return moduleFactory


def memoize(func):
    cache = {}

    def wrapped(*args, **kwargs):
        key = (tuple(args), tuple(kwargs.items()))
        if key not in cache:
            cache[key] = func(*args, **kwargs)
        return cache[key]

    return wrapped