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The problem is is. Is it not?

This has been a re­peat­ed dis­cus­sion in the Python Ar­genti­na mail­ing list. Since it has not come up in a while, why not re­cap it, so the next time it hap­pens peo­ple can just link here.

Some peo­ple for some rea­son do this:

>>> a = 2
>>> b = 2
>>> a == b
>>> a is b

And then, when they do this, they are sur­prised:

>>> a = 1000
>>> b = 1000
>>> a == b
>>> a is b

They are sur­prised be­cause "2 is 2" makes more in­tu­itive sense than "1000 is not 1000". This could be at­trib­uted to an in­cli­na­tion to­wards pla­ton­is­m, but re­al­ly, it's be­cause they don't know what is is.

The is op­er­a­tor is (on CPython) sim­ply a mem­o­ry ad­dress com­par­i­son. if ob­jects a and b are the same ex­act chunk of mem­o­ry, then they "are" each oth­er. Since python pre-cre­ates a bunch of small in­te­gers, then ev­ery 2 you cre­ate is re­al­ly not a new 2, but the same 2 of last time.

This works be­cause of two things:

  1. In­­te­gers are read­­-on­­ly ob­­jec­t­s. You can have as many var­i­ables "hold­ing" the same 2, be­­cause they can't break it.

  2. In python, as­sign­­ment is just alias­ing. You are not mak­ing a copy of 2 when you do a = 2, you are just say­ing "a is an­oth­er name for this 2 here".

This is sur­pris­ing for peo­ple com­ing from oth­er lan­guages, like, say, C or C++. In those lan­guages, a vari­able int a will nev­er use the same mem­o­ry space as an­oth­er vari­able int b be­cause a and b are names for spe­cif­ic bytes of mem­o­ry, and you can change the con­tents of those bytes. On C and C++, in­te­gers are a mu­ta­ble type. This 2 is not that 2, un­less you do it in­ten­tion­al­ly us­ing point­er­s.

In fac­t, the way as­sign­ment works on Python al­so leads to oth­er sur­pris­es, more in­ter­est­ing in re­al life. For ex­am­ple, look at this ses­sion:

>>> def f(s=""):
...     s+='x'
...     return s
>>> f()
>>> f()
>>> f()

That is re­al­ly not sur­pris­ing. Now, let's make a very small change:

>>> def f(l=[]):
...     l.append('x')
...     return l
>>> f()
>>> f()
['x', 'x']
>>> f()
['x', 'x', 'x']

And that is, for some­one who has not seen it be­fore, sur­pris­ing. It hap­pens be­cause lists are a mu­ta­ble type. The de­fault ar­gu­ment is de­fined when the func­tion is parsed, and ev­ery time you call f() you are us­ing and re­turn­ing the same l. Be­fore, you were al­so us­ing al­ways the same s but since strings are im­mutable, it nev­er changed, and you were re­turn­ing a new string each time.

You could check that I am telling you the truth, us­ing is, of course. And BTW, this is not a prob­lem just for list­s. It's a prob­lem for ob­jects of ev­ery class you cre­ate your­self, un­less you both­er mak­ing it im­mutable some­how. So let's be care­ful with de­fault ar­gu­ments, ok?

But the main problem about finding the original 1000 is not 1000 thing surprising is that, in truth, it's uninteresting. Integers are fungible. You don't care if they are the same integer, you only really care that they are equal.

Test­ing for in­te­ger iden­ti­ty is like wor­ry­ing, af­ter you loan me $1, about whether I re­turn you a dif­fer­ent or the same $1 coin. It just does­n't mat­ter. What you want is just a $1 coin, or a 2, or a 1000.

Al­so, the re­sult of 2 is 2 is im­ple­men­ta­tion de­pen­den­t. There is no rea­son, be­yond an op­ti­miza­tion, for that to be True.

Hop­ing this was clear, let me give you a last snip­pet:

>>> a = float('NaN')
>>> a is a
>>> a == a

UP­DATE: lots of fun and in­ter­est­ing com­ments about this post at red­dit and a small fol­lowup here


Hel­lo, my name is Rober­to Alsi­na. You may know me from my ap­pear­ances in "KDE De­vel­op­ers in the Stone Age" and "PyQt pro­gram­mers gone wild".

On the oth­er hand, I am not:

  • Rober­­to Al­si­­na, who lives in Hous­­ton and is ac­­tive in the Ar­­gen­­tine ex­­pa­tri­ate com­­mu­ni­­ty.

  • Ama­­do Rober­­to Al­si­­na, paraguayan poli­ti­­cian.

  • Rober­­to Ariel Al­si­­na (a­­ka Rober­s­tor­m) who drives a mo­­tor­­cy­­cle.

  • Rober­­to Al­si­­na, puer­­tor­i­­can ar­chi­tec­t.

  • Rober­­to Al­si­­na, who lives in Vil­la Ale­m­ana and at­­tend­ed Cole­­gio Buck­­ing­ham.

  • Rober­­to Al­si­­na Ruibal, who I hope is wear­ing a wig.

  • Rober­­to Gon­za­­les Al­si­­na, who lives in Canelones. I on­­ly eat canelones.

  • The FEARED Rober­­to Na­­va Al­si­­na who, while on­­ly 15 years old, is scor­ing goals in some am­a­­teur league some­where.

  • Rober­­to Le­bron Al­si­­na (I have slight­­ly more hair)

  • Rober­­to An­­to­nio Gómez Al­si­­na, ac­­tivist against bul­l­­fight­­ing

Hope­ful­ly, this will clear things up. Thanks for read­ing.

Re-Editar Drácula: Proyecto que me gustaría que alguien agarre.

This post makes no sense in en­glish, so span­ish on­ly!

Drácu­la es un li­bro muy par­tic­u­lar. Casi to­do el mun­do cree que sabe de qué se trata, pero en el 90% de los ca­sos no es así. O sea, sí, saben que es de un vam­piro, blabla.

Lo que no saben es na­da del li­bro. Saben de las pelícu­las, del es­pe­cial de Scoo­by Doo, de­los chistes de vam­piros, y cosas así, pero el li­bro en sí, no lo han leí­do.

¡Y es una lás­ti­ma! Es un li­bro muy in­tere­sante. Para la época que se pub­licó, tiene un es­ti­lo dinámi­co y poco ver­bor­rági­co. Es­tá lleno de ac­ción, es­ce­nas mem­o­rables (no es raro que se hayan he­cho tan­tas pelícu­las), per­son­ajes in­tere­santes. ¡Y enci­ma es un li­bro tec­nó­filo! No es una lec­tura forza­da leer Drácu­la co­mo una mi­cro-­ex­pre­sión de la lucha en­tre la cien­cia y la téc­ni­ca pos­i­tivista con­tra la cul­tura me­dieval reac­cionar­i­a, o cosas así.

Y en­ton­ces, cuan­do el otro día ví, en Work of Art (un re­al­i­ty), a un­os dis­eñadores crear tapas para Drácu­la, se me ocur­rió:

Edite­mos Drácu­la

Agar­remos el orig­i­nal, que es de do­minio públi­co, hag­amos una tra­duc­ción mod­er­na, hag­amos ebook­s, y quién te dice, una edi­ción en pa­pel. Re­galé­mosle a la gente la posi­bil­i­dad de leer una ver­sión mod­er­na de este li­bro buenísi­mo. Una tra­duc­ción que no sea cas­ti­za, ni dé vergüen­za hablan­do de "esto­fa­do con pol­vo de pimien­to ro­jo" si no que di­ga goulash, o por lo menos "esto­fa­do con pa­prika".

Yo ten­go un po­quito de can­cha ha­cien­do type­set­ting de li­bros. Se­guro que se puede con­seguir ilustrador/a/es co­pado/a/as/os para la tapa, tí­tu­los (¡o para ilus­trar in­ter­cal­ado!)

Y... lo mejor es que:

  1. Es un li­bro rel­a­ti­­va­­mente cor­­to

  2. Es­­tá es­­crito en muchas vo­ces dis­­t­in­­tas. No es­­­taría buenísi­­mo que Mi­­na Hark­er lo es­­cri­­ba una mu­­jer? Que Van Hel­s­ing es­­cri­­ba to­­tal­­mente dis­­t­in­­to que Lucy?

En­ton­ces: se nece­si­tan muchas cosas, pero más que nada, se nece­si­tan tra­duc­tores.

¿Quién quiere salir en la tapa de este li­bro? ¿Quién quiere traer al autén­ti­co Drácu­la, el vam­piro en se­ri­o, un autén­ti­co ma­cho de los cár­patos, de vuelta a la vi­da?

Anótense en los co­men­tar­ios.

Living in Zork

You are in an open field west of a big white house with a boarded
front door.

There is a small mailbox here.


We live in the gold­en age of tex­t. Peo­ple write more than ev­er be­fore. Peo­ple read more than ev­er be­fore. On­ly a few short years ago, the pre­ferred mech­a­nism to con­tact oth­er peo­ple was voice based "phone call­s". How quaint that ap­pears to the mod­ern per­son, that types mes­sages through any of to­day's jun­gle of mesag­ing sys­tem­s.

Sure, we al­so take more pic­tures than ev­er be­fore. And more video than ev­er be­fore. Be­cause we are, in gen­er­al, in an in­for­ma­tion gold­en age. But peo­ple ex­pect­ed that.

Who ex­pect­ed, 20 years ago, that kids would pre­fer to type short mes­sages to each oth­er in­stead of hav­ing long phone call­s? Who ex­pect­ed that peo­ple would want to read the mes­sages they got, in­stead of lis­ten­ing to them? Or watch­ing them?

Which is strange, since for as long as I have a mem­o­ry, I have been read­ing that the younger folks can't read or write as well as the old­est gen­er­a­tions (of which I am now part of). The dread­ed lack of "writ­ten text com­pre­hen­sion", mean­ing kids sim­ply did not un­der­stand what the heck they were read­ing. Sure, they could form the words in their mind­s, but the com­plex as­pects (plot, etc) sim­ply did­n't catch.

But why are those kids who could not read writ­ing and read­ing so much? Is that a para­dox? Or is it just that they didn care about what they were read­ing, and when, lat­er in life, they de­cid­ed to pay at­ten­tion, they did get it?

Or maybe it is that un­der­stand­ing long plots is not what read­ing is about nowa­days. That read­ing is about get­ting many small nuggets of data, and the whole cor­re­la­tion is done in our head­s, in­stead of hav­ing it spelled out in long, com­pre­hen­sive texts.

> open mailbox

Opening the mailbox reveals:
A leaflet.

Maybe the prob­lem with long texts and read­ing com­pre­hen­sion is that they are too spe­cif­ic. Once you ex­plain ev­ery­thing, maybe it's bor­ing, and peo­ple's mind wan­der of­f. Maybe you need to keep things short and open-end­ed. Maybe the read­er wants to fill in the blanks.

> read leaflet

Welcome to Zork (originally Dungeon)!

Dungeon is a game of adventure, danger, and low cunning. In it
you will explore some of the most amazing territory ever seen by
mortal man. Hardened adventurers have run screaming from the
terrors contained within.

So, maybe the right way to write in the 21st cen­tu­ry is short and evoca­tive, in­stead of clever and wordy. Maybe the gam­ing com­po­nent of read­ing needs to be amped up, and the us­er will win imag­i­nary badges when­ev­er he gets some in­sight from what he is read­ing, like one of those what­ev­ervilles that give you mean­ing­less awards for mean­ing­less tasks ac­com­plished with mean­ing­less ef­fort.

> go west

You are in a forest, with trees in all directions around you.

Or maybe it's the oth­er way around. Maybe read­ing (or writ­ing) is be­com­ing split in­to two dif­fer­ent things. Maybe we are de­vel­op­ing a high and a low read­ing. A high read­ing that is what tra­di­tion­al­ly was called read­ing, and a low read­ing that is short and func­tion­al and not all that in­ter­est­ing.

> go west


And maybe this means we will get things like Chi­na Miéville's nov­el­s, full of weird for weird's sake, and fun, and things like twit­ter, snip­pets full of whim­sy and con­nec­tion and wit (hey, I fol­low in­ter­est­ing peo­ple), and blogs full of dis­joint­ed mis­ce­lanea, and 9gag full of things that should not, in all hon­esty, be fun­ny.

> reset

Starting over.

PS: http://www.crazygames.­com/game/­zork

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