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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 upload_file(self, metadata, filename, signer=None, sign_password=None, filetype='sdist', pyversion='source', keystore=None):
 """ Upload a release file to the index. :param metadata: A :class:`Metadata` instance defining at least a name and version number for the file to be uploaded. :param filename: The pathname of the file to be uploaded. :param signer: The identifier of the signer of the file. :param sign_password: The passphrase for the signer's private key used for signing. :param filetype: The type of the file being uploaded. This is the distutils command which produced that file, e.g. ``sdist`` or ``bdist_wheel``. :param pyversion: The version of Python which the release relates to. For code compatible with any Python, this would be ``source``, otherwise it would be e.g. ``3.2``. :param keystore: The path to a directory which contains the keys used in signing. If not specified, the instance's ``gpg_home`` attribute is used instead. :return: The HTTP response received from PyPI upon submission of the request. """

        self.check_credentials()
        if not os.path.exists(filename):
            raise DistlibException('not found: %s' % filename)
        metadata.validate()
        d = metadata.todict()
        sig_file = None
        if signer:
            if not self.gpg:
                logger.warning('no signing program available - not signed')
            else:
                sig_file = self.sign_file(filename, signer, sign_password,
                                          keystore)
        with open(filename, 'rb') as f:
            file_data = f.read()
        md5_digest = hashlib.md5(file_data).hexdigest()
        sha256_digest = hashlib.sha256(file_data).hexdigest()
        d.update({
            ':action': 'file_upload',
            'protcol_version': '1',
            'filetype': filetype,
            'pyversion': pyversion,
            'md5_digest': md5_digest,
            'sha256_digest': sha256_digest,
        })
        files = [('content', os.path.basename(filename), file_data)]
        if sig_file:
            with open(sig_file, 'rb') as f:
                sig_data = f.read()
            files.append(('gpg_signature', os.path.basename(sig_file),
                         sig_data))
            shutil.rmtree(os.path.dirname(sig_file))
        request = self.encode_request(d.items(), files)
        return self.send_request(request)