打印到标准输出时的python输出与存储在字典中的输出不同 [英] python output different when printed to std out than stored in dict

问题描述

我正在尝试使用 dnspython 进行区域传输，然后将 A 记录存储到我可以稍后从中弹出值的字典中.见下图:

导入 dns.zone导入 dns.query从 dns.exception 导入 DNSException从 dns.rdataclass 导入 *从 dns.rdatatype 导入 *域 = "mydomain.com"ns = '1.2.3.4'尝试:zone = dns.zone.from_xfr(dns.query.xfr(ns, domain))打印区域原点:"，zone.origin除了 DNSException，e:打印 e.__class__, e对于 zone.iterate_rdatas('A') 中的 (name, ttl, rdata):记录 = { 名称:rdata }打印名称，rdata打印记录

为什么当我使用 print 时的输出与我在字典中存储相同的变量 name, rdata 并打印该 dict 时的输出不同?见下面的输出:

www 1.1.1.1{<DNS 名称 www>:<DNS IN A rdata:1.1.1.1>}

我想澄清我的问题:我如何使字典看起来像:{ 'www' : '1.1.1.1' }

解决方案

发生这种情况是因为 dict 的内容是通过在其每个键/值上调用 repr 来表示的，而打印一个对象直接会调用str.

示例:

<预><代码>>>>弗雷德班级:... def __repr__(self):...返回repr 返回的值"... def __str__(self):...返回str返回的值"...>>>d = {1:弗雷德()}>>>打印{1:repr 返回的值}>>>打印 d[1]str 返回的值

对此您无能为力……您可以编写自己的类版本并定义__repr__，使其与__str__ 的行为相同.或者您可以编写一个自定义的 dict 打印函数来呈现 __str__ 而不是 __repr__ 的结果.但是没有内置的方法可以强制 print somedict 使用 __str__ 而不是 __repr__.

<预><代码>>>>打印 "{" + ", ".join("{} : {}".format(repr(str(key)), repr(str(value))) for key, value in d.iteritems()) + "}"{'1' : 'str 返回的值'}

I'm trying to do a zonetransfer with dnspython, and then store the A record's into a dictionary that i can pop values from later. See below:

import dns.zone
import dns.query
from dns.exception import DNSException
from dns.rdataclass import *
from dns.rdatatype import *

domain = "mydomain.com"
ns = '1.2.3.4'

try:
    zone = dns.zone.from_xfr(dns.query.xfr(ns, domain))
    print "Zone origin:", zone.origin
except DNSException, e:
    print e.__class__, e

for (name, ttl, rdata) in zone.iterate_rdatas('A'):
    record = { name : rdata }
    print name, rdata
    print record

why is the output when i use print is different than when i store the same variables name, rdata in a dictionary, and print that dict? See output below:

www 1.1.1.1
{<DNS name www>: <DNS IN A rdata: 1.1.1.1>}

I guess to clarify my question: How do I make the dict look like : { 'www' : '1.1.1.1' }

解决方案

This is happening because the contents of a dict are represented by calling repr on each of its keys/values, whereas printing an object directly will call str.

Example:

>>> class Fred:
...     def __repr__(self):
...         return "value returned by repr"
...     def __str__(self):
...         return "value returned by str"
...
>>> d = {1: Fred()}
>>> print d
{1: value returned by repr}
>>> print d[1]
value returned by str

There's not a whole lot you can do about this... You could write your own version of the classes you're trying to print and define __repr__ so it behaves identically to __str__. Or you could write a custom dict-printing function that renders the result of __str__ instead of __repr__. But there's no built-in way to force print somedict to use __str__ instead of __repr__.

>>> print "{" + ", ".join("{} : {}".format(repr(str(key)), repr(str(value))) for key, value in d.iteritems()) + "}"
{'1' : 'value returned by str'}

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