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Re: what does 'a=b=c=[]' do

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On Wed, 21 Dec 2011 14:25:17 -0800 (PST), Eric <einazaki668@yahoo.com>
wrote:


>Except it seems that I didn't create three different arrays, I created
>one array that goes by three different names (i.e. x[], y[] and z[]
>all reference the same pile of numbers, no idea which pile).
>
>This surprises me, can someone tell me why it shouldn't?  I figure if
>I want to create and initialize three scalars the just do "a=b=c=7",
>for example, so why not extend it to arrays.  Also, is there a more
>pythonic way to do "x=[], y=[], z=[]"?
>
>It's a slick language but I still have trouble wrapping my brain
>around some of the concepts.
>
	The key one is that lists ([] defines a list, not an array) are
"mutable". Your "7" is not mutable.

	a = b = c = 7
does the same thing as
	a = b = c = []
which is to define the names "a", "b", and "c", and connects the three
names to the single object (integer 7 or new empty list).

	b = 8
then /disconnects/ the name "b" from the object (empty list or integer
7) and connects the name to an integer 8 object.

	b = [1, 2, 3]
disconnects the name "b" from the object and connects it to a list
object containing three elements.

	b.append("something")
however is going "inside" the object to change what it contains -- the
connection remains the same object however.

>>> a,b,c=[[] for x in range(3)]
>>> a.append(1)
>>> b
[]
>>> c
[]
>>> a
[1]
>>>

	For the amount of typing, it's easier to just do a straight line
tuple unpack

>>> a,b,c = ([],[],[])
>>> a.append(2)
>>> a
[2]
>>> b
[]
>>> c
[]
>>>

-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
        wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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what does 'a=b=c=[]' do Eric <einazaki668@yahoo.com> - 2011-12-21 14:25 -0800
  Re: what does 'a=b=c=[]' do Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-12-21 18:20 -0500
    Re: what does 'a=b=c=[]' do Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-21 23:48 +0000
      Re: what does 'a=b=c=[]' do Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-12-24 19:41 +0100
        Re: what does 'a=b=c=[]' do Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-25 13:16 +0000
    Re: what does 'a=b=c=[]' do Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-12-24 19:45 +0100
  Re: what does 'a=b=c=[]' do Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-21 23:44 +0000
    Re: what does 'a=b=c=[]' do Eric <einazaki668@yahoo.com> - 2011-12-22 20:27 -0800
  Re: what does 'a=b=c=[]' do alex23 <wuwei23@gmail.com> - 2011-12-21 16:50 -0800
    Re: what does 'a=b=c=[]' do Rolf Camps <rolf@roce.be> - 2011-12-22 09:51 +0100
      Re: what does 'a=b=c=[]' do alex23 <wuwei23@gmail.com> - 2011-12-22 18:10 -0800
        Re: what does 'a=b=c=[]' do Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-22 19:59 -0700
          Re: what does 'a=b=c=[]' do alex23 <wuwei23@gmail.com> - 2011-12-22 19:40 -0800
            Re: what does 'a=b=c=[]' do Chris Angelico <rosuav@gmail.com> - 2011-12-23 15:25 +1100
            Re: what does 'a=b=c=[]' do Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-22 22:22 -0700
              Re: what does 'a=b=c=[]' do alex23 <wuwei23@gmail.com> - 2011-12-22 22:00 -0800
        Re: what does 'a=b=c=[]' do rusi <rustompmody@gmail.com> - 2011-12-23 00:38 -0800
          Re: what does 'a=b=c=[]' do Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-23 09:39 +0000
            Re: what does 'a=b=c=[]' do rusi <rustompmody@gmail.com> - 2011-12-23 02:22 -0800
              Re: what does 'a=b=c=[]' do Robert Kern <robert.kern@gmail.com> - 2011-12-23 13:10 +0000
                Re: what does 'a=b=c=[]' do rusi <rustompmody@gmail.com> - 2011-12-23 05:23 -0800
                Re: what does 'a=b=c=[]' do Robert Kern <robert.kern@gmail.com> - 2011-12-23 13:53 +0000
                Re: what does 'a=b=c=[]' do rusi <rustompmody@gmail.com> - 2011-12-23 06:57 -0800
                Re: what does 'a=b=c=[]' do Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-23 15:33 +0000
                Re: what does 'a=b=c=[]' do rusi <rustompmody@gmail.com> - 2011-12-23 07:59 -0800
          Re: what does 'a=b=c=[]' do Ethan Furman <ethan@stoneleaf.us> - 2011-12-23 00:49 -0800
          Re: what does 'a=b=c=[]' do Chris Angelico <rosuav@gmail.com> - 2011-12-23 20:59 +1100
            Re: what does 'a=b=c=[]' do rusi <rustompmody@gmail.com> - 2011-12-23 02:31 -0800
              Timeout when calling COM objects on Windows Wong Wah Meng-R32813 <r32813@freescale.com> - 2011-12-23 11:20 +0000
              Re: what does 'a=b=c=[]' do Michael Torrie <torriem@gmail.com> - 2011-12-23 10:23 -0700
            Re: what does 'a=b=c=[]' do Neil Cerutti <neilc@norwich.edu> - 2011-12-23 13:10 +0000
              Re: what does 'a=b=c=[]' do Neil Cerutti <neilc@norwich.edu> - 2011-12-23 13:13 +0000
                Early and late binding [was Re: what does 'a=b=c=[]' do] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-23 15:49 +0000
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Chris Angelico <rosuav@gmail.com> - 2011-12-24 02:55 +1100
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-23 22:32 +0000
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Chris Angelico <rosuav@gmail.com> - 2011-12-24 09:50 +1100
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-24 08:11 +0000
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Roy Smith <roy@panix.com> - 2011-12-23 11:15 -0500
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] alex23 <wuwei23@gmail.com> - 2011-12-24 05:43 -0800
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Mel Wilson <mwilson@the-wire.com> - 2011-12-23 11:27 -0500
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] alex23 <wuwei23@gmail.com> - 2011-12-24 05:52 -0800
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Neil Cerutti <neilc@norwich.edu> - 2011-12-23 17:03 +0000
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-24 08:25 +0000
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] alex23 <wuwei23@gmail.com> - 2011-12-24 06:08 -0800
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-12-24 18:25 -0500
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] alex23 <wuwei23@gmail.com> - 2011-12-24 16:10 -0800
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-12-24 19:32 -0500
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] rusi <rustompmody@gmail.com> - 2011-12-24 19:22 -0800
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Lie Ryan <lie.1296@gmail.com> - 2011-12-25 15:12 +1100
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-12-23 19:24 -0500
                Re: Early and late binding [was Re: what does 'a=b=c=[]' do] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-24 08:26 +0000
        Re: what does 'a=b=c=[]' do Ethan Furman <ethan@stoneleaf.us> - 2011-12-23 00:38 -0800
    Re: what does 'a=b=c=[]' do Ethan Furman <ethan@stoneleaf.us> - 2011-12-22 05:20 -0800
    Re: what does 'a=b=c=[]' do Eric <einazaki668@yahoo.com> - 2011-12-22 19:46 -0800
  Re: what does 'a=b=c=[]' do Lie Ryan <lie.1296@gmail.com> - 2011-12-24 21:30 +1100
  Re: what does 'a=b=c=[]' do Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-12-24 19:49 +0100

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