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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 from_file(cls, source, distance_weights=None, merge_same_words=False, group_marker_opening='<<', group_marker_closing='>>'):
 """ Read a string from a file and derive a ``Graph`` from it. This is a convenience function for opening a file and passing its contents to ``Graph.from_string()`` (see that for more detail) Args: source (str):
 the file to read and derive the graph from distance_weights (dict):
 dict of relative indices corresponding with word weights. See ``Graph.from_string`` for more detail. merge_same_words (bool):
 whether nodes which have the same value should be merged or not. group_marker_opening (str):
 The string used to mark the beginning of word groups. group_marker_closing (str):
 The string used to mark the end of word groups. Returns: Graph Example: 'poetry i have nothing to say and i' """

        source_string = open(source, 'r').read()
        return cls.from_string(source_string,
                               distance_weights,
                               merge_same_words,
                               group_marker_opening=group_marker_opening,
                               group_marker_closing=group_marker_closing)