def install(self, source, dest=None, checksum=None, hash_type='sha1'):
        """
        Download and install an archive file, with optional checksum validation.

        The checksum can also be given on the `source` URL's fragment.
        For example::

            handler.install('http://example.com/file.tgz#sha1=deadbeef')

        :param str source: URL pointing to an archive file.
        :param str dest: Local destination path to install to. If not given,
            installs to `$CHARM_DIR/archives/archive_file_name`.
        :param str checksum: If given, validate the archive file after download.
        :param str hash_type: Algorithm used to generate `checksum`.
            Can be any hash alrgorithm supported by :mod:`hashlib`,
            such as md5, sha1, sha256, sha512, etc.

        """
        url_parts = self.parse_url(source)
        dest_dir = os.path.join(os.environ.get('CHARM_DIR'), 'fetched')
        if not os.path.exists(dest_dir):
            mkdir(dest_dir, perms=0o755)
        dld_file = os.path.join(dest_dir, os.path.basename(url_parts.path))
        try:
            self.download(source, dld_file)
        except URLError as e:
            raise UnhandledSource(e.reason)
        except OSError as e:
            raise UnhandledSource(e.strerror)
        options = parse_qs(url_parts.fragment)
        for key, value in options.items():
            if not six.PY3:
                algorithms = hashlib.algorithms
            else:
                algorithms = hashlib.algorithms_available
            if key in algorithms:
                if len(value) != 1:
                    raise TypeError(
                        "Expected 1 hash value, not %d" % len(value))
                expected = value[0]
                check_hash(dld_file, expected, key)
        if checksum:
            check_hash(dld_file, checksum, hash_type)
        return extract(dld_file, dest)
Download and install an archive file, with optional checksum validation.

        The checksum can also be given on the `source` URL's fragment.
        For example::

            handler.install('http://example.com/file.tgz#sha1=deadbeef')

        :param str source: URL pointing to an archive file.
        :param str dest: Local destination path to install to. If not given,
            installs to `$CHARM_DIR/archives/archive_file_name`.
        :param str checksum: If given, validate the archive file after download.
        :param str hash_type: Algorithm used to generate `checksum`.
            Can be any hash alrgorithm supported by :mod:`hashlib`,
            such as md5, sha1, sha256, sha512, etc.