__init__.py

import sys

PY3 = sys.version_info[0] == 3
PY2 = sys.version_info[0] == 2
PYPY = hasattr(sys, 'pypy_translation_info')

def with_metaclass(meta, *bases):
    """
    Function from jinja2/_compat.py. License: BSD.

    Use it like this::
        
        class BaseForm(object):
            pass
        
        class FormType(type):
            pass
        
        class Form(with_metaclass(FormType, BaseForm)):
            pass

    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 of not introducing
    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, {})


def native(obj):
    """
    On Py2, this is a no-op: native(obj) -> obj

    On Py3, returns the corresponding native Py3 types that are
    superclasses for forward-ported objects from Py2:
    
    >>> from past.builtins import str, dict

    >>> native(str(b'ABC'))   # Output on Py3 follows. On Py2, output is 'ABC'
    b'ABC'
    >>> type(native(str(b'ABC')))
    bytes

    Existing native types on Py3 will be returned unchanged:

    >>> type(native(b'ABC'))
    bytes
    """
    if hasattr(obj, '__native__'):
        return obj.__native__()
    else:
        return obj



__all__ = ['PY3', 'PY2', 'PYPY', 'with_metaclass', 'native']