def execd_module_paths(execd_dir=None):
    """Generate a list of full paths to modules within execd_dir."""
    if not execd_dir:
        execd_dir = default_execd_dir()

    if not os.path.exists(execd_dir):
        return

    for subpath in os.listdir(execd_dir):
        module = os.path.join(execd_dir, subpath)
        if os.path.isdir(module):
            yield module
Generate a list of full paths to modules within execd_dir.