AttributeError: ‘str’ object has no attribute ‘write’

I’m working on Python and have defined a variable called “_headers” as shown below

_headers = ('id',
                'recipient_address_1',
                'recipient_address_2',
                'recipient_address_3',
                'recipient_address_4',
                'recipient_address_5',
                'recipient_address_6',
                'recipient_postcode',
                )

and in order to write this into an output file, I’ve written the following statement but it throws me the error “AttributeError: ‘str’ object has no attribute ‘write'”

with open(outfile, 'w') as f:  
            outfile.write(self._headers)  
            print done

Please help