Re: meaning of: line, =

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Date	Fri, 6 Feb 2015 12:17:31 +1100
Subject	Re: meaning of: line, =
From	Chris Angelico <rosuav@gmail.com>
To	Python <python-list@python.org>
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On Fri, Feb 6, 2015 at 12:12 PM, Devin Jeanpierre
<jeanpierreda@gmail.com> wrote:
> Here's another example, one that still exists in Python 3:
>
>>>> [] = ''
>>>> () = ''
>   File "<stdin>", line 1
> SyntaxError: can't assign to ()
>
> The syntax explicitly blacklists (), but forgets to blacklist [].

So... this is actually a really really obscure little feature.

[] = x
# is equivalent to
try: next(iter(x))
except StopIteration: pass
else: raise ValueError("too many values to unpack (expected 0)")

It's a way of asserting that an iterator is exhausted! Perfect code
snippet for your next International Obfuscated Python Code Contest
entry.

ChrisA

Thread

Re: meaning of: line, = Albert-Jan Roskam <fomcl@yahoo.com> - 2015-02-04 14:38 +0000
  Re: meaning of: line, = Rustom Mody <rustompmody@gmail.com> - 2015-02-04 07:09 -0800
    Re: meaning of: line, = Peter Otten <__peter__@web.de> - 2015-02-04 18:36 +0100
    Re: meaning of: line, = Chris Angelico <rosuav@gmail.com> - 2015-02-05 08:18 +1100
    Re: meaning of: line, = Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-02-05 01:10 -0800
      Re: meaning of: line, = Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-05 20:40 +1100
        Re: meaning of: line, = Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-05 09:08 -0700
          Re: meaning of: line, = Rustom Mody <rustompmody@gmail.com> - 2015-02-05 08:45 -0800
            Re: meaning of: line, = Skip Montanaro <skip.montanaro@gmail.com> - 2015-02-05 10:56 -0600
            Re: meaning of: line, = Tim Chase <python.list@tim.thechases.com> - 2015-02-05 11:00 -0600
            Re: meaning of: line, = Rustom Mody <rustompmody@gmail.com> - 2015-02-05 08:59 -0800
              Re: meaning of: line, = Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-02-06 05:09 -0800
                Re: meaning of: line, = Rustom Mody <rustompmody@gmail.com> - 2015-02-06 05:20 -0800
                Re: meaning of: line, = Rustom Mody <rustompmody@gmail.com> - 2015-02-06 06:03 -0800
        Re: meaning of: line, = Tim Chase <python.list@tim.thechases.com> - 2015-02-05 10:21 -0600
        Re: meaning of: line, = Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-02-05 17:12 -0800
        Re: meaning of: line, = Chris Angelico <rosuav@gmail.com> - 2015-02-06 12:17 +1100
          Re: meaning of: line, = Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-02-06 17:52 +1300
      Re: meaning of: line, = Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-02-06 12:30 +1300

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