Find all module files in the given folder that end with '.py' and
    don't start with an underscore.
    @return module names
    @rtype: iterator of string

def get_importable_modules(folder):
    """Find all module files in the given folder that end with '.py' and
    don't start with an underscore.
    @return module names
    @rtype: iterator of string
    """
    for fname in os.listdir(folder):
        if fname.endswith('.py') and not fname.startswith('_'):
            yield fname[:-3]