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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 __isValidTGZ(self, suffix):

 """To determine whether the suffix `.tar.gz` or `.tgz` format"""

        if suffix and isinstance(suffix, string_types):
            if suffix.endswith(".tar.gz") or suffix.endswith(".tgz"):
                return True
        return False