Return a name, unique within a context, based on the specified name.

    @param base: the desired base name of the generated unique name.
    @param existing: a sequence of the existing names to avoid returning.
    @param format: a formatting specification for how the name is made unique.

def make_unique_name(base, existing=[], format="%s_%s"):
    """ Return a name, unique within a context, based on the specified name.

    @param base: the desired base name of the generated unique name.
    @param existing: a sequence of the existing names to avoid returning.
    @param format: a formatting specification for how the name is made unique.
    """
    count = 2
    name = base
    while name in existing:
        name = format % (base, count)
        count += 1

    return name