Python新手关于元组的问题

发布于 2024-07-09 07:37:40 字数 1255 浏览 7 评论 0原文

我是 Python 新手，正在使用 cx_Oracle 模块编写一些数据库代码。在cx_Oracle文档中，他们有一个如下的代码示例：

import sys
import cx_Oracle

connection = cx_Oracle.Connection("user/pw@tns")
cursor = connection.cursor()

try:
    cursor.execute("select 1 / 0 from dual")
except cx_Oracle.DatabaseError, exc:
    error, = exc.args
    print >> sys.stderr, "Oracle-Error-Code:", error.code
    print >> sys.stderr, "Oracle-Error-Message:", error.message

我的问题必须处理创建“错误”对象的位置。 “,=”有什么作用？我尝试搜索 Python 文档，当您搜索运算符时，搜索引擎不能很好地工作。 :-)

我知道 exc.args 是一个单例元组，但我只是不理解“, =”语法。如果删除逗号，则会收到错误消息“AttributeError: 'tuple' object has no attribute 'code'”。

有人可以指出我的记录在哪里吗？谢谢！

编辑：

这无需解压元组即可工作：

import sys
import cx_Oracle

connection = cx_Oracle.Connection("user/pw@tns")
cursor = connection.cursor()

try:
    cursor.execute("select 1 / 0 from dual")
except cx_Oracle.DatabaseError, exc:
    print >> sys.stderr, "Oracle-Error-Code:", exc.args[0].code
    print >> sys.stderr, "Oracle-Error-Message:", exc.args[0].message

原文

I am new to Python, and I'm working on writing some database code using the cx_Oracle module. In the cx_Oracle documentation they have a code example like this:

import sys
import cx_Oracle

connection = cx_Oracle.Connection("user/pw@tns")
cursor = connection.cursor()

try:
    cursor.execute("select 1 / 0 from dual")
except cx_Oracle.DatabaseError, exc:
    error, = exc.args
    print >> sys.stderr, "Oracle-Error-Code:", error.code
    print >> sys.stderr, "Oracle-Error-Message:", error.message

My question has to do with where the "error" object is created. What does the ", =" do? I tried searching Python documentation, and search engines don't work very well when you're searching for operators. :-)

I know that the exc.args is a singleton tuple, but I just don't understand the ", =" syntax. If I remove the comma, I get the error message, "AttributeError: 'tuple' object has no attribute 'code'".

Can someone point me to where this is documented? Thanks!

EDIT:

This works without having to unpack the tuple:

import sys
import cx_Oracle

connection = cx_Oracle.Connection("user/pw@tns")
cursor = connection.cursor()

try:
    cursor.execute("select 1 / 0 from dual")
except cx_Oracle.DatabaseError, exc:
    print >> sys.stderr, "Oracle-Error-Code:", exc.args[0].code
    print >> sys.stderr, "Oracle-Error-Message:", exc.args[0].message

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未蓝澄海的烟 2024-07-16 07:37:40

error, = exc.args

这是序列解包的情况。

一种更易读的编写方式，也是我个人喜欢的风格，是：

[error] = exc.args

理解前面的示例需要两个位：

当赋值的左侧是名称的递归序列时，右侧的值side 必须是长度相同的序列，并且将 RHS 值的每一项分配给 LHS 中对应的名称。
Python 中的单项元组写作 (foo,)。在大多数情况下，可以省略括号。特别是，可以在赋值运算符旁边省略它们。

error, = exc.args

This is a case of sequence unpacking.

A more readable way to write the same, and the style I personally favor, is:

[error] = exc.args

There are two bits required to understand the previous example:

When the left hand side of an assignment is a recursive sequence of names, the value of the right hand side must be a sequence with the same length, and each item of the RHS value is assigned to the corresponding name in the LHS.
A one-item tuple in python is written (foo,). In most contexts, the parenthesis can be ommitted. In particular, they can be omitted next to the assignment operator.

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