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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 get_header(self, hdrclass, returnval=None):
        '''
        Return the first header object that is of
        class hdrclass, or None if the header class isn't
        found.
        '''
        if isinstance(hdrclass, str):
            return self.get_header_by_name(hdrclass)

        for hdr in self._headers:
            if isinstance(hdr, hdrclass):
                return hdr
        return returnval