"""

Providing iterator functions that are not in all version of Python we support.

Where possible, we try to use the system-native version and only fall back to

these implementations if necessary.

"""

import itertools

def compat_tee(iterable):

    """

    Return two independent iterators from a single iterable.

    Based on http://www.python.org/doc/2.3.5/lib/itertools-example.html

    """

    # Note: Using a dictionary and a list as the default arguments here is

    # deliberate and safe in this instance.

    def gen(next, data={}, cnt=[0]):

        dpop = data.pop

        for i in itertools.count():

            if i == cnt[0]:

                item = data[i] = next()

                cnt[0] += 1

            else:

                item = dpop(i)

            yield item

    next = iter(iterable).next

    return gen(next), gen(next)

def groupby(iterable, keyfunc=None):

    """

    Taken from http://docs.python.org/lib/itertools-functions.html

    """

    if keyfunc is None:

        keyfunc = lambda x:x

    iterable = iter(iterable)

    l = [iterable.next()]

    lastkey = keyfunc(l[0])

    for item in iterable:

        key = keyfunc(item)

        if key != lastkey:

            yield lastkey, l

            lastkey = key

            l = [item]

        else:

            l.append(item)

    yield lastkey, l

# Not really in itertools, since it's a builtin in Python 2.4 and later, but it

# does operate as an iterator.

def reversed(data):

    for index in xrange(len(data)-1, -1, -1):

        yield data[index]

if hasattr(itertools, 'tee'):

    tee = itertools.tee

else:

    tee = compat_tee

if hasattr(itertools, 'groupby'):

    groupby = itertools.groupby

def is_iterable(x):

    "A implementation independent way of checking for iterables"

    try:

        iter(x)

    except TypeError:

        return False

    else:

        return True

def sorted(in_value):

    "A naive implementation of sorted"

    out_value = in_value[:]

    out_value.sort()

    return out_value