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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 _sign_file(self, file, default_key=None, passphrase=None, clearsign=True, detach=False, binary=False, digest_algo='SHA512'):
 """Create a signature for a file. :param file: The file stream (i.e. it's already been open()'d) to sign. :param str default_key: The key to sign with. :param str passphrase: The passphrase to pipe to stdin. :param bool clearsign: If True, create a cleartext signature. :param bool detach: If True, create a detached signature. :param bool binary: If True, do not ascii armour the output. :param str digest_algo: The hash digest to use. Again, to see which hashes your GnuPG is capable of using, do: ``$ gpg --with-colons --list-config digestname``. The default, if unspecified, is ``'SHA512'``. """

        log.debug("_sign_file():")
        if binary:
            log.info("Creating binary signature for file %s" % file)
            args = ['--sign']
        else:
            log.info("Creating ascii-armoured signature for file %s" % file)
            args = ['--sign --armor']

        if clearsign:
            args.append("--clearsign")
            if detach:
                log.warn("Cannot use both --clearsign and --detach-sign.")
                log.warn("Using default GPG behaviour: --clearsign only.")
        elif detach and not clearsign:
            args.append("--detach-sign")

        if default_key:
            args.append(str("--default-key %s" % default_key))

        args.append(str("--digest-algo %s" % digest_algo))

        ## We could use _handle_io here except for the fact that if the
        ## passphrase is bad, gpg bails and you can't write the message.
        result = self._result_map['sign'](self)

        ## If the passphrase is an empty string, the message up to and
        ## including its first newline will be cut off before making it to the
        ## GnuPG process. Therefore, if the passphrase='' or passphrase=b'',
        ## we set passphrase=None.  See Issue #82:
        ## https://github.com/isislovecruft/python-gnupg/issues/82
        if _util._is_string(passphrase):
            passphrase = passphrase if len(passphrase) > 0 else None
        elif _util._is_bytes(passphrase):
            passphrase = s(passphrase) if len(passphrase) > 0 else None
        else:
            passphrase = None

        proc = self._open_subprocess(args, passphrase is not None)
        try:
            if passphrase:
                _util._write_passphrase(proc.stdin, passphrase, self._encoding)
            writer = _util._threaded_copy_data(file, proc.stdin)
        except IOError as ioe:
            log.exception("Error writing message: %s" % str(ioe))
            writer = None
        self._collect_output(proc, result, writer, proc.stdin)
        return result