Method add_done_callback

Lib/asyncio/futures.py:226–238

Add a callback to be run when the future becomes done. The callback is called with a single argument - the future object. If the future is already done when this is called, the callback is scheduled with call_soon.

(self, fn, *, context=None)

        return self._exception

    def add_done_callback(self, fn, *, context=None):
        """Add a callback to be run when the future becomes done.

        The callback is called with a single argument - the future object. If
        the future is already done when this is called, the callback is
        scheduled with call_soon.
        """
        if self._state != _PENDING:
            self._loop.call_soon(fn, self, context=context)
        else:
            if context is None:
                context = contextvars.copy_context()
            self._callbacks.append((fn, context))

    # New method not in PEP 3148.