列表理解 [英] list comprehension
问题描述
您好，
尝试更改字符串（x，y值），例如：
s =" 114320,69808 114272 ，69920 113568,71600 113328,72272
到（x，-y）：
out =" 114320，-69808 114272 ，-69920 113568，-71600 113328，-72272"
我试过这个：
print [（a [0]， - a [1] for x.split（''，''））for x in e]
但它不起作用。任何人都可以建议为什么或建议另一种方式
方式？文字字符串比这大得多，所以表演
很重要。
TIA，
Guy
文章< c7 ********** @ lust.ihug.co.nz>，
Guy Robinson< gu*@NOSPAM.red.co.nz>写道：
尝试更改字符串（x，y值），例如：
s =" 114320,69808 114272,69920 113568,71600 113328 ，72272
到（x，-y）：
out =" 114320，-69808 114272，-69920 113568，-71600 113328，-72272"
我试过这个：
打印[（a [0]， - a [1] for x.split（''，''））for x in e]
但它不起作用。任何人都可以建议为什么或建议另类
方式？文本字符串比这大得多，所以性能很重要。
如有疑问，请将问题分成更小的步骤。让我玩Socrates
一分钟：使用数据集的第一步是什么？
-
Aahz（aa **@pythoncraft.com）< *> http://www.pythoncraft.com/
采用流程 - 停止杀死所有孩子！
这项工作我只是想知道是否可以写更多内容
简明扼要希望更快：
s =" 114320,69808 114272,69920 113568,71600 113328,72272"
e = s.split（''''）
out =''''
for d in e：
d = d.split（''，''）
out + =''％s，％d''％（d [0]， - int（d [1]））
打印出来
Guy
Aahz写道：
文章< c7 ********** @ lust。 ihug.co.nz>，
Guy Robinson< gu*@NOSPAM.red.co.nz>写道：
试图更改字符串（x，y值），例如：
s =" 114320,69808 114272,69920 113568,71600 113328 ，72272
到（x，-y）：
out =" 114320，-69808 114272，-69920 113568，-71600 113328，-72272"
我试过这个：
打印[（a [0]， - a [1] for x.split（''，''））for x in e]
但它不起作用。任何人都可以建议为什么或建议另类
方式？文本字符串比这大得多，因此性能很重要。
如有疑问，请将问题分解为更小的步骤。让我玩Socrates
一分钟：使用数据集的第一步是什么？
5月10日星期一， 2004年12:32:20 PM +1200，Guy Robinson写道：你好，
试图改变一个字符串（x，y值），如：
对于（x，-y）：
out =" 114320 ，-69808 114272，-69920 113568，-71600 113328，-72272"
我试过这个：
打印[（a [0]， - a [1] for a in x.split（''，''）for x in e]
但它不起作用。任何人都可以建议为什么或建议另类
方式？文本字符串比这大得多，所以性能很重要。
它有几个语法错误; （a [0]， - a [1] for x.split（''，''））不是
有效表达式，因为列表推导被方括号括起来
括号，而不是括号。此外，列表理解的第一部分，
计算每个元素的表达式，如果它具有
a逗号，则需要在parens中，以便解析器可以消除歧义它来自一个普通的清单。
我也不知道你从哪里来的'e''。它是'''，还是's.split（）''？
如果列表comprenhensions变得笨拙，只需使用for循环。他们可能比一个列表理解更容易阅读，这需要你花十分钟时间来完成，并且性能几乎完全相同。然而，为了回答你的问题，这里的表达符合你的要求：
< blockquote class =post_quotes> s =" 114320,69808 114272,69920 113568,71600 113328,72272"
s.replace（''，''，''， - ''）
' '114320，-69808 114272，-69920 113568，-71600 113328，-72272''
你可以用列表推导来做到这一点，例如：
' '''.join（[''％s， - ％s''％tuple（x）代表[pair.split（''，''）中x对于s.split（''''）]中的对）
''114320，-69808 114272，-69920 113568，-71600 113328，-72272''
但是我没有看到这一点，因为你已经描述了
问题。
-Andrew。
Hello,
Trying to change a string(x,y values) such as :
s = "114320,69808 114272,69920 113568,71600 113328,72272"
into (x,-y):
out = "114320,-69808 114272,-69920 113568,-71600 113328,-72272"
I tried this:
print [(a[0],-a[1] for a in x.split('','')) for x in e]
But it doesn''t work. Can anyone suggest why or suggest an alternative
way? The text strings are significantly bigger than this so performance
is important.
TIA,
Guy
In article <c7**********@lust.ihug.co.nz>,
Guy Robinson <gu*@NOSPAM.r-e-d.co.nz> wrote:
Trying to change a string(x,y values) such as :
s = "114320,69808 114272,69920 113568,71600 113328,72272"
into (x,-y):
out = "114320,-69808 114272,-69920 113568,-71600 113328,-72272"
I tried this:
print [(a[0],-a[1] for a in x.split('','')) for x in e]
But it doesn''t work. Can anyone suggest why or suggest an alternative
way? The text strings are significantly bigger than this so performance
is important.
When in doubt, break a problem into smaller steps. Let me play Socrates
for a minute: what''s the first step in working with your dataset?
--
Aahz (aa**@pythoncraft.com) <*> http://www.pythoncraft.com/
Adopt A Process -- stop killing all your children!
This works I was just wondering if something could be written more
concisely and hopefully faster:
s = "114320,69808 114272,69920 113568,71600 113328,72272"
e = s.split('' '')
out =''''
for d in e:
d =d.split('','')
out +=''%s,%d '' %(d[0],-int(d[1]))
print out
Guy
Aahz wrote:
In article <c7**********@lust.ihug.co.nz>,
Guy Robinson <gu*@NOSPAM.r-e-d.co.nz> wrote:Trying to change a string(x,y values) such as :
s = "114320,69808 114272,69920 113568,71600 113328,72272"
into (x,-y):
out = "114320,-69808 114272,-69920 113568,-71600 113328,-72272"
I tried this:
print [(a[0],-a[1] for a in x.split('','')) for x in e]
But it doesn''t work. Can anyone suggest why or suggest an alternative
way? The text strings are significantly bigger than this so performance
is important.
When in doubt, break a problem into smaller steps. Let me play Socrates
for a minute: what''s the first step in working with your dataset?
On Mon, May 10, 2004 at 12:32:20PM +1200, Guy Robinson wrote:Hello,
Trying to change a string(x,y values) such as :
s = "114320,69808 114272,69920 113568,71600 113328,72272"
into (x,-y):
out = "114320,-69808 114272,-69920 113568,-71600 113328,-72272"
I tried this:
print [(a[0],-a[1] for a in x.split('','')) for x in e]
But it doesn''t work. Can anyone suggest why or suggest an alternative
way? The text strings are significantly bigger than this so performance
is important.
It has several syntax errors; (a[0],-a[1] for a in x.split('','')) is not a
valid expression because list comprehensions are bracketed by square
brackets, not parentheses. Also, the first part of a list comprehension,
the expression to calculate each element, needs to be in parens to if it has
a comma, so that the parser can disambiguate it from an ordinary list.
I also don''t know where you got ''e'' from. Is it ''s'', or ''s.split()''?
If list comprenhensions grow unwieldy, just use a for loop. They''re
probably easier to read than a list comprehension that takes you ten minutes
to concoct, and performance is almost identical. For the sake of answering
your question, though, here''s a expression that does what you ask:
s = "114320,69808 114272,69920 113568,71600 113328,72272"
s.replace('','','',-'') ''114320,-69808 114272,-69920 113568,-71600 113328,-72272''
You could do this with list comprehensions, e.g.:
'' ''.join([''%s,-%s'' % tuple(x) for x in [pairs.split('','') for pairs in s.split('' '')]])
''114320,-69808 114272,-69920 113568,-71600 113328,-72272''
But I don''t really see the point, given the way you''ve described the
problem.
-Andrew.
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