def identity(what):
    return what


def first(iterable, predicate=identity):
    if iterable:
        for x in iterable:
            if predicate(x):
                return x
    return None


def to_string(ints):
    return ','.join(str(i) for i in ints)


def to_ints(string):
    """ Transform a string of comma-separated integers into a list of ints.
    """
    ints = list()
    for s in string.split(','):
        try:
            ints.append(int(s))
        except ValueError:
            pass
    return ints