list of the lists - append after search

Andrew Zyman formisc at gmail.com
Fri Mar 3 13:58:43 EST 2017


On Thursday, March 2, 2017 at 3:53:25 PM UTC-5, Andrew Zyman wrote:
> On Thursday, March 2, 2017 at 3:31:36 PM UTC-5, Jussi Piitulainen wrote:
> > Andrew Zyman writes:
> > 
> > > On Thursday, March 2, 2017 at 2:57:02 PM UTC-5, Jussi Piitulainen wrote:
> > >> Peter Otten <__peter__ at web.de> writes:
> > >> 
> > >> > Andrew Zyman wrote:
> > >> >
> > >> >> On Thursday, March 2, 2017 at 11:27:34 AM UTC-5, Peter Otten wrote:
> > >> >>> Andrew Zyman wrote:
> > >> >>> .....
> > >> >>> .....
> > >> >>> > End result:
> > >> >>> >  ll =[ [a,1], [b,2], [c,3], [blah, 1000, 'new value'] ]
> > >> >>> 
> > >> >>> >>> outer = [["a", 1], ["b", 2], ["c", 3], ["blah", 1000]]
> > >> >>> >>> for inner in outer:
> > >> >>> ...     if inner[0] == "blah":
> > >> >>> ...         inner.append("new value")
> > >> >> 
> > >> >> thank you. this will do.
> > >> >> Just curious, is the above loop can be done in a one-liner?
> > >> >
> > >> > Ah, that newbie obsession ;)
> > >> >
> > >> >>>> outer = [["a", 1], ["b", 2], ["c", 3], ["blah", 1000]]
> > >> >>>> [inner + ["new value"] if inner[0] == "blah" else inner for inner in 
> > >> > outer]
> > >> > [['a', 1], ['b', 2], ['c', 3], ['blah', 1000, 'new value']]
> > >> >
> > >> > Note that there is a technical difference to be aware of -- matching
> > >> > lists are replaced rather than modified.
> > >> 
> > >> I take it you are too sane, or too kind, to suggest the obvious
> > >> solution:
> > >> 
> > >> >>> outer = [["a", 1], ["b", 2], ["c", 3], ["blah", 1000]]
> > >> >>> [inner.append("new value") for inner in outer if inner[0] == "blah"]
> > >> [None]
> > >> >>> outer
> > >> [['a', 1], ['b', 2], ['c', 3], ['blah', 1000, 'new value']]
> > >> 
> > >> [snip]
> > >
> > > Arh!!! this is it :)
> > >
> > > I'm sure i'll regret this line of code in 2 weeks - after i
> > > successfully forget what i wanted to achieve :)
> > 
> > Jokes aside, you should strive to express your intention in your code.
> > Be kind to your future self. Write the three-line loop if you want
> > in-place modification.
> > 
> > I use comprehensions a lot, but not to save lines. I might make Peter's
> > expression above a four-liner to make its structure more visible:
> > 
> >   res = [ ( inner + ["new value"]
> >             if inner[0] == "blah"
> >             else inner )
> >           for inner in outer ]
> > 
> > Maybe.
> 
> thank you gentlemen. This is very helpful discussion and i appreciate your explanations - helped a lot.


Well, i'll take my earlier statement ( about using lists ) back . 100K search/expend on list is taking way too much time ( over 4 minutes ).  i'll follow your advice and move the processing to dict.
Thanx again.


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