Get the hash of some data, using a particular hash algorithm, if
        specified.

        :param data: The data to be hashed.
        :type data: bytes
        :param hasher: The name of a hash implementation, supported by hashlib,
                       or ``None``. Examples of valid values are ``'sha1'``,
                       ``'sha224'``, ``'sha384'``, '``sha256'``, ``'md5'`` and
                       ``'sha512'``. If no hasher is specified, the ``hasher``
                       attribute of the :class:`InstalledDistribution` instance
                       is used. If the hasher is determined to be ``None``, MD5
                       is used as the hashing algorithm.
        :returns: The hash of the data. If a hasher was explicitly specified,
                  the returned hash will be prefixed with the specified hasher
                  followed by '='.
        :rtype: str

def get_hash(self, data, hasher=None):
        """
        Get the hash of some data, using a particular hash algorithm, if
        specified.

        :param data: The data to be hashed.
        :type data: bytes
        :param hasher: The name of a hash implementation, supported by hashlib,
                       or ``None``. Examples of valid values are ``'sha1'``,
                       ``'sha224'``, ``'sha384'``, '``sha256'``, ``'md5'`` and
                       ``'sha512'``. If no hasher is specified, the ``hasher``
                       attribute of the :class:`InstalledDistribution` instance
                       is used. If the hasher is determined to be ``None``, MD5
                       is used as the hashing algorithm.
        :returns: The hash of the data. If a hasher was explicitly specified,
                  the returned hash will be prefixed with the specified hasher
                  followed by '='.
        :rtype: str
        """
        if hasher is None:
            hasher = self.hasher
        if hasher is None:
            hasher = hashlib.md5
            prefix = ''
        else:
            hasher = getattr(hashlib, hasher)
            prefix = '%s=' % self.hasher
        digest = hasher(data).digest()
        digest = base64.urlsafe_b64encode(digest).rstrip(b'=').decode('ascii')
        return '%s%s' % (prefix, digest)