How to use the diffoscope.changes.ChangesFileException function in diffoscope

"Unknown problem while verifying signature")

        # contains verbose human readable GPG information
        gpg_output_stderr = str(gpg_output_stderr, encoding='utf8')
        print(gpg_output_stderr)

        gpg_output = gpg_output.decode(encoding='UTF-8')

        if gpg_output.count('[GNUPG:] GOODSIG'):
            pass
        elif gpg_output.count('[GNUPG:] BADSIG'):
            raise ChangesFileException("Bad signature")
        elif gpg_output.count('[GNUPG:] ERRSIG'):
            raise ChangesFileException("Error verifying signature")
        elif gpg_output.count('[GNUPG:] NODATA'):
            raise ChangesFileException("No signature on")
        else:
            raise ChangesFileException(
                "Unknown problem while verifying signature"
            )

        key = None
        for line in gpg_output.split("\n"):
            if line.startswith('[GNUPG:] VALIDSIG'):
                key = line.split()[2]
        return key

# contains verbose human readable GPG information
        gpg_output_stderr = str(gpg_output_stderr, encoding='utf8')
        print(gpg_output_stderr)

        gpg_output = gpg_output.decode(encoding='UTF-8')

        if gpg_output.count('[GNUPG:] GOODSIG'):
            pass
        elif gpg_output.count('[GNUPG:] BADSIG'):
            raise ChangesFileException("Bad signature")
        elif gpg_output.count('[GNUPG:] ERRSIG'):
            raise ChangesFileException("Error verifying signature")
        elif gpg_output.count('[GNUPG:] NODATA'):
            raise ChangesFileException("No signature on")
        else:
            raise ChangesFileException(
                "Unknown problem while verifying signature"
            )

        key = None
        for line in gpg_output.split("\n"):
            if line.startswith('[GNUPG:] VALIDSIG'):
                key = line.split()[2]
        return key

if pipe.returncode != 0:
            raise ChangesFileException(
                "Unknown problem while verifying signature")

        # contains verbose human readable GPG information
        gpg_output_stderr = str(gpg_output_stderr, encoding='utf8')
        print(gpg_output_stderr)

        gpg_output = gpg_output.decode(encoding='UTF-8')

        if gpg_output.count('[GNUPG:] GOODSIG'):
            pass
        elif gpg_output.count('[GNUPG:] BADSIG'):
            raise ChangesFileException("Bad signature")
        elif gpg_output.count('[GNUPG:] ERRSIG'):
            raise ChangesFileException("Error verifying signature")
        elif gpg_output.count('[GNUPG:] NODATA'):
            raise ChangesFileException("No signature on")
        else:
            raise ChangesFileException(
                "Unknown problem while verifying signature"
            )

        key = None
        for line in gpg_output.split("\n"):
            if line.startswith('[GNUPG:] VALIDSIG'):
                key = line.split()[2]
        return key

print(gpg_output)

        if pipe.returncode != 0:
            raise ChangesFileException(
                "Unknown problem while verifying signature")

        # contains verbose human readable GPG information
        gpg_output_stderr = str(gpg_output_stderr, encoding='utf8')
        print(gpg_output_stderr)

        gpg_output = gpg_output.decode(encoding='UTF-8')

        if gpg_output.count('[GNUPG:] GOODSIG'):
            pass
        elif gpg_output.count('[GNUPG:] BADSIG'):
            raise ChangesFileException("Bad signature")
        elif gpg_output.count('[GNUPG:] ERRSIG'):
            raise ChangesFileException("Error verifying signature")
        elif gpg_output.count('[GNUPG:] NODATA'):
            raise ChangesFileException("No signature on")
        else:
            raise ChangesFileException(
                "Unknown problem while verifying signature"
            )

        key = None
        for line in gpg_output.split("\n"):
            if line.startswith('[GNUPG:] VALIDSIG'):
                key = line.split()[2]
        return key

if changed_files['name'] == os.path.basename(filename):
                    break
            else:
                assert(
                    "get_files() returns different files than Files: knows?!")

            with open(os.path.join(self._directory, filename), "rb") as fc:
                while True:
                    chunk = fc.read(131072)
                    if not chunk:
                        break
                    hash_type.update(chunk)
            fc.close()

            if not hash_type.hexdigest() == changed_files[field_name]:
                raise ChangesFileException(
                    "Checksum mismatch for file %s: %s != %s" % (
                        filename,
                        hash_type.hexdigest(),
                        changed_files[field_name]
                    ))
            else:
                logger.debug("%s Checksum for file %s matches",
                    field_name, filename)

def validate_signature(self, check_signature=True):
        """
        Validate the GPG signature of a .changes file.

        Throws a :class:`dput.exceptions.ChangesFileException` if there's
        an issue with the GPG signature. Returns the GPG key ID.
        """
        pipe = subprocess.Popen(
            ["gpg", "--status-fd", "1", "--verify", "--batch",
             self.get_changes_file()],
            shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        gpg_output, gpg_output_stderr = pipe.communicate()
        print(gpg_output)

        if pipe.returncode != 0:
            raise ChangesFileException(
                "Unknown problem while verifying signature")

        # contains verbose human readable GPG information
        gpg_output_stderr = str(gpg_output_stderr, encoding='utf8')
        print(gpg_output_stderr)

        gpg_output = gpg_output.decode(encoding='UTF-8')

        if gpg_output.count('[GNUPG:] GOODSIG'):
            pass
        elif gpg_output.count('[GNUPG:] BADSIG'):
            raise ChangesFileException("Bad signature")
        elif gpg_output.count('[GNUPG:] ERRSIG'):
            raise ChangesFileException("Error verifying signature")
        elif gpg_output.count('[GNUPG:] NODATA'):
            raise ChangesFileException("No signature on")

``string``
            *changes* file in a string to parse.
        """
        if (filename and string) or (not filename and not string):
            raise TypeError

        if filename:
            self._absfile = os.path.abspath(filename)
            self._directory = os.path.dirname(self._absfile)
            self._data = deb822.Changes(open(filename, encoding='utf-8'))
            self.basename = os.path.basename(filename)
        else:
            self._data = deb822.Changes(string)

        if len(self._data) == 0:
            raise ChangesFileException('Changes file could not be parsed.')