Class _Placeholder

test/mitmproxy/proxy/tutils.py:365–401

Placeholder value in playbooks, so that objects (flows in particular) can be referenced before they are known. Example: f = Placeholder(TCPFlow) assert ( playbook(tcp.TCPLayer(tctx)) << TcpStartHook(f) # the flow object returned here is generated by the layer.

class _Placeholder(Generic[T]):
    """
    Placeholder value in playbooks, so that objects (flows in particular) can be referenced before
    they are known. Example:

    f = Placeholder(TCPFlow)
    assert (
        playbook(tcp.TCPLayer(tctx))
        << TcpStartHook(f)  # the flow object returned here is generated by the layer.
    )

    # We can obtain the flow object now using f():
    assert f().messages == 0
    """

    def __init__(self, cls: type[T]):
        self._obj = None
        self._cls = cls

    def __call__(self) -> T:
        """Get the actual object"""
        return self._obj

    def setdefault(self, value: T) -> T:
        if self._obj is None:
            if self._cls is not Any and not isinstance(value, self._cls):
                raise TypeError(
                    f"expected {self._cls.__name__}, got {type(value).__name__}."
                )
            self._obj = value
        return self._obj

    def __repr__(self):
        return f"Placeholder:{self._obj!r}"

    def __str__(self):
        return f"Placeholder:{self._obj}"


# noinspection PyPep8Naming