list comprehension

[Peter Otten]

Tim Roberts wrote:

> Guy Robinson <guy at NOSPAM.r-e-d.co.nz> wrote:
> 
>>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
> 
> Well, why not the more obvious:  s.replace(',',',-')

But beware negative numbers:

>>> int("--1")
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: invalid literal for int(): --1
>>>

Therefore at least

>>> "123,234 567,-789".replace(",", ",-").replace("--", "")
'123,-234 567,789'
>>>

As to robustness, the OP relying on commas not being followed by a space
seems dangerous, too, if the original data is created manually.

Peter