Return True if `path` is a directory containing a setup.py file.

def is_installable_dir(path):
    """Return True if `path` is a directory containing a setup.py file."""
    if not os.path.isdir(path):
        return False
    setup_py = os.path.join(path, "setup.py")
    if os.path.isfile(setup_py):
        return True
    return False