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我知道 is 用于比较两个对象是否相同，而 == 用于相等。根据我的经验， 是 总是适用于数字，因为 Python 重用了数字。例如:
>>>a = 3
>>>a is 3
True
每当我将某物与数字进行比较时，我习惯使用 is。但是 is 不适用于下面的这个程序:
from collections import namedtuple
# Code taken directly from [Udacity site][1].
# make a basic Link class
Link = namedtuple('Link', ['id', 'submitter_id', 'submitted_time', 'votes',
'title', 'url'])
# list of Links to work with
links = [
Link(0, 60398, 1334014208.0, 109,
"C overtakes Java as the No. 1 programming language in the TIOBE index.",
"http://pixelstech.net/article/index.php?id=1333969280"),
Link(1, 60254, 1333962645.0, 891,
"This explains why technical books are all ridiculously thick and overpriced",
"http://prog21.dadgum.com/65.html"),
Link(23, 62945, 1333894106.0, 351,
"Learn Haskell Fast and Hard",
"http://yannesposito.com/Scratch/en/blog/Haskell-the-Hard-Way/"),
Link(2, 6084, 1333996166.0, 81,
"Announcing Yesod 1.0- a robust, developer friendly, high performance web framework for Haskell",
"http://www.yesodweb.com/blog/2012/04/announcing-yesod-1-0"),
Link(3, 30305, 1333968061.0, 270,
"TIL about the Lisp Curse",
"http://www.winestockwebdesign.com/Essays/Lisp_Curse.html"),
Link(4, 59008, 1334016506.0, 19,
"The Downfall of Imperative Programming. Functional Programming and the Multicore Revolution",
"http://fpcomplete.com/the-downfall-of-imperative-programming/"),
Link(5, 8712, 1333993676.0, 26,
"Open Source - Twitter Stock Market Game - ",
"http://www.twitstreet.com/"),
Link(6, 48626, 1333975127.0, 63,
"First look: Qt 5 makes JavaScript a first-class citizen for app development",
"http://arstechnica.com/business/news/2012/04/an-in-depth-look-at-qt-5-making-javascript-a-first-class-citizen-for-native-cross-platform-developme.ars"),
Link(7, 30172, 1334017294.0, 5,
"Benchmark of Dictionary Structures", "http://lh3lh3.users.sourceforge.net/udb.shtml"),
Link(8, 678, 1334014446.0, 7,
"If It's Not on Prod, It Doesn't Count: The Value of Frequent Releases",
"http://bits.shutterstock.com/?p=165"),
Link(9, 29168, 1334006443.0, 18,
"Language proposal: dave",
"http://davelang.github.com/"),
Link(17, 48626, 1334020271.0, 1,
"LispNYC and EmacsNYC meetup Tuesday Night: Large Scale Development with Elisp ",
"http://www.meetup.com/LispNYC/events/47373722/"),
Link(101, 62443, 1334018620.0, 4,
"research!rsc: Zip Files All The Way Down",
"http://research.swtch.com/zip"),
Link(12, 10262, 1334018169.0, 5,
"The Tyranny of the Diff",
"http://michaelfeathers.typepad.com/michael_feathers_blog/2012/04/the-tyranny-of-the-diff.html"),
Link(13, 20831, 1333996529.0, 14,
"Understanding NIO.2 File Channels in Java 7",
"http://java.dzone.com/articles/understanding-nio2-file"),
Link(15, 62443, 1333900877.0, 1244,
"Why vector icons don't work",
"http://www.pushing-pixels.org/2011/11/04/about-those-vector-icons.html"),
Link(14, 30650, 1334013659.0, 3,
"Python - Getting Data Into Graphite - Code Examples",
"http://coreygoldberg.blogspot.com/2012/04/python-getting-data-into-graphite-code.html"),
Link(16, 15330, 1333985877.0, 9,
"Mozilla: The Web as the Platform and The Kilimanjaro Event",
"https://groups.google.com/forum/?fromgroups#!topic/mozilla.dev.planning/Y9v46wFeejA"),
Link(18, 62443, 1333939389.0, 104,
"github is making me feel stupid(er)",
"http://www.serpentine.com/blog/2012/04/08/github-is-making-me-feel-stupider/"),
Link(19, 6937, 1333949857.0, 39,
"BitC Retrospective: The Issues with Type Classes",
"http://www.bitc-lang.org/pipermail/bitc-dev/2012-April/003315.html"),
Link(20, 51067, 1333974585.0, 14,
"Object Oriented C: Class-like Structures",
"http://cecilsunkure.blogspot.com/2012/04/object-oriented-c-class-like-structures.html"),
Link(10, 23944, 1333943632.0, 188,
"The LOVE game framework version 0.8.0 has been released - with GLSL shader support!",
"https://love2d.org/forums/viewtopic.php?f=3&t=8750"),
Link(22, 39191, 1334005674.0, 11,
"An open letter to language designers: Please kill your sacred cows. (megarant)",
"http://joshondesign.com/2012/03/09/open-letter-language-designers"),
Link(21, 3777, 1333996565.0, 2,
"Developers guide to Garage48 hackatron",
"http://martingryner.com/developers-guide-to-garage48-hackatron/"),
Link(24, 48626, 1333934004.0, 17,
"An R programmer looks at Julia",
"http://www.r-bloggers.com/an-r-programmer-looks-at-julia/")]
# links is a list of Link objects. Links have a handful of properties. For
# example, a Link's number of votes can be accessed by link.votes if "link" is a
# Link.
# make the function query() return a list of Links submitted by user 62443, by
# submission time ascending
def query():
print "hello"
print [link for link in links if link.submitter_id == 62443] # is does not work
return sorted([link for link in links if link.submitter_id == 62443],key = lambda x: x[2])
query()
当我像这样在查询函数中使用 is 时 [link for link in links if link.submitter_id is 62443] 我会得到一个空列表。但是如果我使用 ==，它工作正常。
在大多数情况下，代码是直接从 udacity 站点获取的，但我也在我的本地机器上尝试过。同样的结果。所以我认为在这种情况下数字现在是不同的对象，但为什么呢？有这个必要吗？
编辑:是的。我承认这个问题是重复的，应该关闭。但它与 first post 重复不是the second .在发布之前我不知道这个问题。
我的问题是我认为数字对象总是会被重用。
多亏了大家，我改掉了一个坏习惯。