生成器表达式不具备列表推导能力吗？ [英] What's do list comprehensions do that generator expressions don't?
问题描述
好的，我们已经在语言中添加了列表推导，并且看到了
它们很好。我们已经为语言添加了生成器表达式，并且看到它们也很好。$ / b
我有点困惑，虽然 - 如果我打算要求2.4，我什么时候才能使用list comp而不是
生成器表达式？
谢谢，
< mike
-
Mike Meyer< mw*@mired.org> http://www.mired.org/home/mwm/
独立的WWW / Perforce / FreeBSD / Unix顾问，电子邮件以获取更多信息。
Ok, we''ve added list comprehensions to the language, and seen that
they were good. We''ve added generator expressions to the language, and
seen that they were good as well.
I''m left a bit confused, though - when would I use a list comp instead
of a generator expression if I''m going to require 2.4 anyway?
Thanks,
<mike
--
Mike Meyer <mw*@mired.org> http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.
推荐答案
Mike Meyer写道：
Mike Meyer wrote:
好的，我们已经在语言中添加了列表推导，并且看到它们很好。我们已经在语言中添加了生成器表达式，并且看到它们也很好。
我有点困惑，但是 - 我什么时候会使用列表comp相反，如果我要要求2.4，那么生成器表达式是什么？
Ok, we''ve added list comprehensions to the language, and seen that
they were good. We''ve added generator expressions to the language, and
seen that they were good as well.
I''m left a bit confused, though - when would I use a list comp instead
of a generator expression if I''m going to require 2.4 anyway?
从不。如果你真的需要一个清单
清单（x * x代表xrange（10））
可悲的是，我们不能删除列表推导到3.0。
-
Robert Kern
rk *** @ ucsd.edu
在草地长高的地狱里
是梦的坟墓允许死亡。
- Richard Harter
Never. If you really need a list
list(x*x for x in xrange(10))
Sadly, we can''t remove list comprehensions until 3.0.
--
Robert Kern
rk***@ucsd.edu
"In the fields of hell where the grass grows high
Are the graves of dreams allowed to die."
-- Richard Harter
Robert Kern写道：
Robert Kern wrote:
Mike Meyer写道：
Mike Meyer wrote:
好的，我们已经在语言中添加了列表推导，并且看到它们很好。我们已经在语言中添加了生成器表达式，并且看到它们也很好。
我有点困惑，但是 - 我什么时候会使用列表comp相反，如果我要要求2.4，那么生成器表达式是什么？
Ok, we''ve added list comprehensions to the language, and seen that
they were good. We''ve added generator expressions to the language, and
seen that they were good as well.
I''m left a bit confused, though - when would I use a list comp instead
of a generator expression if I''m going to require 2.4 anyway?
从不。如果你真的需要一个列表
列表（x * x for x in xrange（10））
Never. If you really need a list
list(x*x for x in xrange(10))
不太正确。如果你发现不太可能的场景，即生成器表达式中列表的构造是一个效率
瓶颈，你可以选择一个列表理解 - 它们是略有的
当你真正想要一个列表时更快：
Not quite true. If you discovered the unlikely scenario that the
construction of a list from the generator expression was an efficiency
bottleneck, you might choose a list comprehension -- they''re slightly
faster when you really do want a list:
python -m timeit" list（x * x代表x in xrange（10））"
100000循环，最佳3：每循环使用6.54
python -m timeit "list(x*x for x in xrange(10))"
100000 loops, best of 3: 6.54 usec per loop
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