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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 execute(self, data_dict, callback, group=None, trace=None):
 """Low level method to expand the template piece by piece. Args: data_dict: The JSON data dictionary. callback: A callback which should be called with each expanded token. group: Dictionary of name -> Template instance (for styles) Example: You can pass 'f.write' as the callback to write directly to a file handle. """

        # First try the passed in version, then the one set by _SetTemplateGroup.  May
        # be None.  Only one of these should be set.
        group = group or self.group
        context = _ScopedContext(data_dict, self.undefined_str, group=group)
        _Execute(self._program.Statements(), context, callback, trace)