environment.py 文件源码

def _environment_sanity_check(environment):
    """Perform a sanity check on the environment."""
    assert issubclass(environment.undefined, Undefined), 'undefined must ' \
        'be a subclass of undefined because filters depend on it.'
    assert environment.block_start_string != \
        environment.variable_start_string != \
        environment.comment_start_string, 'block, variable and comment ' \
        'start strings must be different'
    assert environment.newline_sequence in ('\r', '\r\n', '\n'), \
        'newline_sequence set to unknown line ending string.'
    return environment