此处所需的特殊关键字是主机：

The special keyword needed here is host:

DATABASE_URL=postgres://user:password@/dbname?host=/path/to/db

请注意，主机中的路径应该是路径，而不是套接字文件本身（psycopg2假定套接字具有标准命名约定 .s.PGSQL.5432 ）

Note that the path in host should be a path, not the socket file itself (psycopg2 assumes the socket has the standard naming convention .s.PGSQL.5432)

https://docs.sqlalchemy.org/en/latest/dialects/postgresql.html#unix -domain-connections