How to use the dvc.logger.Logger.error function in dvc

if not instance:
            Logger.error('Instance Id is not specified')
            return None

        target_in_active = list(filter(lambda inst: inst.id == instance, active))
        if len(target_in_active) > 0:
            Logger.error('The instance is already active')
            return None

        target_in_not_actives = list(filter(lambda inst: inst.id == instance, not_active))
        if len(target_in_not_actives) == 0:
            Logger.error('The instance is not running')
            return None

        if len(target_in_not_actives) > 1:
            Logger.error('Instances consistancy error: more than one instance with the same id')
            return None

        return target_in_not_actives

def _verify_md5(self, req, fname):
        """
        Verify md5 of a downloaded file if server supports 'content-md5' header.
        """
        md5 = file_md5(fname)[0]
        content_md5 = self._get_header(req, 'content-md5')

        if content_md5 == None:
            return True

        if md5 != content_md5:
            Logger.error('Checksum mismatch')
            return False

        Logger.debug('Checksum matches')
        return True

def unset_target(self, target_conf_file_path):
        if not os.path.exists(target_conf_file_path):
            Logger.error('Target conf file {} does not exists'.format(
                target_conf_file_path))
            return 1
        if not os.path.isfile(target_conf_file_path):
            Logger.error('Target conf file {} exists but it is not a regular file'.format(
                target_conf_file_path))
            return 1
        if open(target_conf_file_path).read() == '':
            return 0

        os.remove(target_conf_file_path)
        open(target_conf_file_path, 'a').close()

        return self.commit_if_needed('DVC target unset')

def _push_key(self, key, path):
        """ push, aws version """
        name = os.path.relpath(path, self._cloud_settings.cache.cache_dir)
        cb = self.create_cb_push(name, path)
        try:
            self.s3.Object(key.bucket, key.name).upload_file(path, Callback=cb)
        except Exception as exc:
            Logger.error('Failed to upload "{}": {}'.format(path, exc))
            return None

        progress.finish_target(name)

        return path

def _get_target_in_not_active(instance, active, not_active):
        if not instance:
            Logger.error('Instance Id is not specified')
            return None

        target_in_active = list(filter(lambda inst: inst.id == instance, active))
        if len(target_in_active) > 0:
            Logger.error('The instance is already active')
            return None

        target_in_not_actives = list(filter(lambda inst: inst.id == instance, not_active))
        if len(target_in_not_actives) == 0:
            Logger.error('The instance is not running')
            return None

        if len(target_in_not_actives) > 1:
            Logger.error('Instances consistancy error: more than one instance with the same id')
            return None

        return target_in_not_actives

def _get_target_in_not_active(instance, active, not_active):
        if not instance:
            Logger.error('Instance Id is not specified')
            return None

        target_in_active = list(filter(lambda inst: inst.id == instance, active))
        if len(target_in_active) > 0:
            Logger.error('The instance is already active')
            return None

        target_in_not_actives = list(filter(lambda inst: inst.id == instance, not_active))
        if len(target_in_not_actives) == 0:
            Logger.error('The instance is not running')
            return None

        if len(target_in_not_actives) > 1:
            Logger.error('Instances consistancy error: more than one instance with the same id')
            return None

        return target_in_not_actives

def _import(self, bucket, i, path):
        inp = os.path.join(self.storage_path, i)
        tmp_file = self.tmp_file(path)
        try:
            copyfile(inp, tmp_file)
        except Exception as exc:
            Logger.error('Failed to copy "{}": {}'.format(i, exc))
            return None

        os.rename(tmp_file, path)

        return path

def _get_target_in_not_active(instance, active, not_active):
        if not instance:
            Logger.error('Instance Id is not specified')
            return None

        target_in_active = list(filter(lambda inst: inst.id == instance, active))
        if len(target_in_active) > 0:
            Logger.error('The instance is already active')
            return None

        target_in_not_actives = list(filter(lambda inst: inst.id == instance, not_active))
        if len(target_in_not_actives) == 0:
            Logger.error('The instance is not running')
            return None

        if len(target_in_not_actives) > 1:
            Logger.error('Instances consistancy error: more than one instance with the same id')
            return None