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Groups > comp.lang.python > #95001
| References | <ebf0a31e-1021-41d2-affb-8318838a464b@googlegroups.com> <631b480d-497a-4451-9577-2788f9d4c85b@googlegroups.com> |
|---|---|
| Date | 2015-08-05 17:20 +1000 |
| Subject | Re: GOTCHA with list comprehension |
| From | Chris Angelico <rosuav@gmail.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.1232.1438759213.3674.python-list@python.org> (permalink) |
On Wed, Aug 5, 2015 at 5:03 PM, Pavel S <pavel@schon.cz> wrote:
> It seems this is allowed by the grammar:
>
> list_display ::= "[" [expression_list | list_comprehension] "]"
> list_comprehension ::= expression list_for
> list_for ::= "for" target_list "in" old_expression_list [list_iter]
> old_expression_list ::= old_expression [("," old_expression)+ [","]]
> old_expression ::= or_test | old_lambda_expr
> list_iter ::= list_for | list_if
> list_if ::= "if" old_expression [list_iter]
>
> So chaining multiple ifs is fine:
>
> [ i for i in range(10) if True if True if True if True ]
Yep. A chain of 'if' clauses isn't materially different from a single
'if' with a bunch of 'and' checks, but if you alternate 'if' and 'for'
clauses, you get a comprehension that conditionally nests its
iterations.
ChrisA
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GOTCHA with list comprehension Pavel S <pavel@schon.cz> - 2015-08-04 23:48 -0700
Re: GOTCHA with list comprehension Pavel S <pavel@schon.cz> - 2015-08-05 00:03 -0700
Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-05 17:20 +1000
Re: GOTCHA with list comprehension Peter Otten <__peter__@web.de> - 2015-08-05 09:04 +0200
Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-05 17:05 +1000
Re: GOTCHA with list comprehension Pavel S <pavel@schon.cz> - 2015-08-05 00:10 -0700
Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-05 17:21 +1000
Re: GOTCHA with list comprehension Pavel S <pavel@schon.cz> - 2015-08-05 00:33 -0700
Re: GOTCHA with list comprehension Marko Rauhamaa <marko@pacujo.net> - 2015-08-05 12:01 +0300
Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-05 19:52 +1000
Re: GOTCHA with list comprehension Marko Rauhamaa <marko@pacujo.net> - 2015-08-05 14:10 +0300
Re: GOTCHA with list comprehension Saran Ahluwalia <ahlusar.ahluwalia@gmail.com> - 2015-08-07 09:08 -0400
Re: GOTCHA with list comprehension Laura Creighton <lac@openend.se> - 2015-08-06 06:39 +0200
Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-06 14:44 +1000
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