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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 do(stream, action, key, default=None, dump=yaml_dump, loader=ShyamlSafeLoader):
 """Return string representations of target value in stream YAML The key is used for traversal of the YAML structure to target the value that will be dumped. :param stream: file like input yaml content :param action: string identifying one of the possible supported actions :param key: string dotted expression to traverse yaml input :param default: optional default value in case of missing end value when traversing input yaml. (default is ``None``) :param dump: callable that will be given python objet to dump in yaml (default is ``yaml_dump``) :param loader: PyYAML's *Loader subclass to parse YAML (default is ShyamlSafeLoader) :return: generator of string representation of target value per YAML docs in the given stream. :raises ActionTypeError: when there's a type mismatch between the action selected and the type of the targetted value. (ie: action 'key-values' on non-struct) :raises InvalidAction: when selected action is not a recognised valid action identifier. :raises InvalidPath: upon inexistent content when traversing YAML input following the key specification. """

    at_least_one_content = False
    for content in yaml.load_all(stream, Loader=loader):
        at_least_one_content = True
        value = traverse(content, key, default=default)
        yield act(action, value, dump=dump)

    ## In case of empty stream, we consider that it is equivalent
    ## to one document having the ``null`` value.
    if at_least_one_content is False:
        value = traverse(None, key, default=default)
        yield act(action, value, dump=dump)