没有 DSN 的 cx_oracle 连接

Question

I am maintaining some code where i came about a curious connection string of following type to an oracle database (from redhat linux):

import cx_Oracle
cx_Oracle.Connection("username/password")

Notably no DSN is specified; User name and password are enough (the connection is working).

How is this possible? How does cx_oracle know where to connect to? Is there some default value/environment variable that is used if no DSN is given? The way I understood the documentation, the DSN is a mandatory argument.

Answer 1

cx_oracle has method to create dsn makedsn

dsn = cx_Oracle.makedsn(host, port, sid=None, service_name=None, region=None, sharding_key=None, super_sharding_key=None)

with cx_Oracle.connect(user=user, password=password,
                       dsn=dsn,
                       encoding="UTF-8") as connection:
    cursor = connection.cursor()
    cursor.execute("insert into SomeTable values (:1, :2)",
                   (1, "Some string"))
    connection.commit()

Answer 2

As Devyl mentioned, if you have ORACLE_SID or TWO_TASK environment variables set, they maybe used to make a connection.

Eg see this answer https://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:89412348059