def __init__(self, enable=None, substitution_tag=None):
self._enable = None<EOL>self._substitution_tag = None<EOL>if enable is not None:<EOL><INDENT>self.enable = enable<EOL><DEDENT>if substitution_tag is not None:<EOL><INDENT>self.substitution_tag = substitution_tag<EOL><DEDENT>
Create an OpenTracking to track when your email is opened.

        :param enable: If open tracking is enabled.
        :type enable: boolean, optional
        :param substitution_tag: Tag in body to be replaced by tracking pixel.
        :type substitution_tag: string, optional