Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Ken Seehart <k.seehart@partner.samsung.com>
Newsgroups: comp.lang.python
Subject: PEP proposal: sequence expansion support for yield statement: yield *
Date: Wed, 20 Apr 2016 19:34:24 +0000
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Thread-topic: PEP proposal: sequence expansion support for yield statement: yield *
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Currently the common pattern for yielding the elements in a sequence is as =
follows:

  for x in sequence: yield x

I propose the following replacement (the result would be identical):

  yield *sequence

The semantics are somewhat different from argument expansion (from which th=
e syntax is borrowed), but intuitive: yield all of the elements of a sequen=
ce (as opposed to yield the sequence as a single item). This doesn't appear=
 to have any syntactical collisions, as it is currently a syntax error.

Motivation: More compact notation, and the compiler can produce more effici=
ent bytecode than the former representation (the loop overhead is omitted).=
 This pattern is very common in recursive generators, so a compact notation=
 would be nice.

Also, there is precedent: the proposed notation is implemented in javascrip=
t with identical semantics (though in javascript, the conventional spacing =
is different: yield* sequence ).

Examples:
  yield *(1,2,3)
... instead of :
  yield 1; yield 2; yield 3
... or:
  for x in (1,2,3): yield x


  yield *chain(seq1, seq2)
... instead of :
  for x in chain(seq1, seq2) yield x

~ Ken Seehart