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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def channel(val: Any, default: Any = RaiseTypeErrorIfNotProvided ) -> Union[Tuple[np.ndarray], Sequence[TDefault]]: r"""Returns a list of matrices describing the channel for the given value. These matrices are the terms in the operator sum representation of then this describes the channel: \rho \rightarrow \sum_{k=0}^{r-1} A_0 \rho A_0^\dagger These matrices are required to satisfy the trace preserving condition \sum_{k=0}^{r-1} A_i^\dagger A_i = I where I is the identity matrix. The matrices A_i are sometimes called Krauss or noise operators. Args: val: The value to describe by a channel. default: Determines the fallback behavior when `val` doesn't have a channel. If `default` is not set, a TypeError is raised. If default is set to a value, that value is returned. Returns: If `val` has a `_channel_` method and its result is not NotImplemented, that result is returned. Otherwise, if `val` has a `_mixture_` method and its results is not NotImplement a tuple made up of channel corresponding to that mixture being a probabilistic mixture of unitaries is returned. Otherwise, if `val` has a `_unitary_` method and its result is not NotImplemented a tuple made up of that result is returned. Otherwise, if a default value was specified, the default value is returned. Raises: TypeError: `val` doesn't have a _channel_ or _unitary_ method (or that method returned NotImplemented) and also no default value was specified. """

    channel_getter = getattr(val, '_channel_', None)
    channel_result = (
        NotImplemented if channel_getter is None else channel_getter())
    if channel_result is not NotImplemented:
        return tuple(channel_result)

    mixture_getter = getattr(val, '_mixture_', None)
    mixture_result = (
        NotImplemented if mixture_getter is None else mixture_getter())
    if mixture_result is not NotImplemented:
        return tuple(np.sqrt(p) * u for p, u in mixture_result)

    unitary_getter = getattr(val, '_unitary_', None)
    unitary_result = (
        NotImplemented if unitary_getter is None else unitary_getter())
    if unitary_result is not NotImplemented:
        return (unitary_result,)

    if default is not RaiseTypeErrorIfNotProvided:
        return default

    if (channel_getter is None and unitary_getter is None
            and mixture_getter is None):
        raise TypeError("object of type '{}' has no _channel_ or _mixture_ or "
                        "_unitary_ method.".format(type(val)))
    raise TypeError("object of type '{}' does have a _channel_, _mixture_ or "
                "_unitary_ method, but it returned NotImplemented."
                .format(type(val)))