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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 validate(self, obj, **kwargs):
 """Check if a thing is a valid domain name."""

        text = stringify(obj)
        if text is None:
            return False
        if '.' not in text:
            return False
        if '@' in text or ':' in text:
            return False
        if len(text) < 4:
            return False
        return True