Run through L{ETREE_MODULES} and find C{ElementTree} implementations so
    that any type can be encoded.

    We work through the C implementations first, then the pure Python versions.
    The downside to this is that B{all} libraries will be imported but I{only}
    one is ever used. The libs are small (relatively) and the flexibility that
    this gives seems to outweigh the cost. Time will tell.

def find_libs():
    """
    Run through L{ETREE_MODULES} and find C{ElementTree} implementations so
    that any type can be encoded.

    We work through the C implementations first, then the pure Python versions.
    The downside to this is that B{all} libraries will be imported but I{only}
    one is ever used. The libs are small (relatively) and the flexibility that
    this gives seems to outweigh the cost. Time will tell.
    """
    from pyamf.util import get_module

    types = []
    mapping = {}

    for mod in ETREE_MODULES:
        try:
            etree = get_module(mod)
        except ImportError:
            continue

        t = _get_etree_type(etree)

        types.append(t)
        mapping[t] = etree

    return tuple(types), mapping