def __init__(self, open_tracking_substitution_tag=None):
self._open_tracking_substitution_tag = None<EOL>if open_tracking_substitution_tag is not None:<EOL><INDENT>self.open_tracking_substitution_tag =open_tracking_substitution_tag<EOL><DEDENT>
Create a OpenTrackingSubstitutionTag object

        :param open_tracking_substitution_tag: Allows you to specify a
            substitution tag that you can insert in the body of your
            email at a location that you desire. This tag will be replaced
            by the open tracking pixel.