meta.py 文件源码

def _is_safe_generator(code):
    '''
    Examine the code of an async generator to see if it appears
    unsafe with respect to async finalization.  A generator
    is unsafe if it utilizes any of the following constructs:

    1. Use of async-code in a finally block

       try:
           yield v
       finally:
           await coro()

    2. Use of yield inside an async context manager

       async with m:
           ...
           yield v
           ...

    3. Use of async-code in try-except

       try:
           yield v
       except Exception:
           await coro()
    '''
    def _is_unsafe_block(instr, end_offset=-1):
        is_generator = False
        in_final = False
        is_unsafe = False
        for op in instr:
            if op.offset == end_offset:
                in_final = True
            if op.opname == 'YIELD_VALUE':
                is_generator = True
            if op.opname == 'END_FINALLY':
                return (is_generator, is_unsafe)
            if op.opname in {'SETUP_FINALLY', 'SETUP_EXCEPT', 'SETUP_ASYNC_WITH'}:
                is_g, is_u = _is_unsafe_block(instr, op.argval)
                is_generator |= is_g
                is_unsafe |= is_u
            if op.opname == 'YIELD_FROM' and is_generator and in_final:
                is_unsafe = True
        return (is_generator, is_unsafe)

    return not _is_unsafe_block(dis.get_instructions(code))[1]