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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 check_checksum_mismatch(self):
        ''' Checking for a checksum that doesn't match the generated checksum '''
        if self.pefile_handle.OPTIONAL_HEADER:
            if self.pefile_handle.OPTIONAL_HEADER.CheckSum != self.pefile_handle.generate_checksum():
                return {'description': 'Reported Checksum does not match actual checksum', 
                        'severity': 2, 'category': 'MALFORMED'}
        return None