printing out elements in list

[micklee74@hotmail.com]

hi

i have a list with contents like this
alist = ['>QWER' , 'askfhs', '>REWR' ,'sfsdf' , '>FGDG',
'sdfsdgffdgfdg' ]

how can i "convert" this list into a dictionary such that

dictionary = { '>QWER':'askfhs ' , '>REWR' : 'sfsdf' , '>FGDG',
'sdfsdgffdgfdg' }

thanks

[Tim N. van der Leeuw]

Re: printing out elements in list

Using slices and built-in zip:
[color=blue][color=green][color=darkred]
>>> alist = ['>QWER' , 'askfhs', '>REWR' ,'sfsdf' , '>FGDG', 'sdfsdgffdgfdg' ]
>>> dict(zip(alist[::2], alist[1::2]))[/color][/color][/color]
{'>QWER': 'askfhs', '>FGDG': 'sdfsdgffdgfdg' , '>REWR': 'sfsdf'}

Slightly more efficient might be to use izip from itertools:
[color=blue][color=green][color=darkred]
>>> from itertools import izip
>>> dict(izip(alist[::2], alist[1::2]))[/color][/color][/color]
{'>QWER': 'askfhs', '>FGDG': 'sdfsdgffdgfdg' , '>REWR': 'sfsdf'}

And perhaps using islice from iterools might improve efficiency even
more:
[color=blue][color=green][color=darkred]
>>> from itertools import islice, izip
>>> dict(izip(islic e(alist, 0, None, 2), islice(alist, 1, None, 2)))[/color][/color][/color]
{'>QWER': 'askfhs', '>FGDG': 'sdfsdgffdgfdg' , '>REWR': 'sfsdf'}


(I didn't try to time any of these solutions so I have no real idea
which is more efficient, but using iterators from the itertools-module
should in theory mean you create less temporary objects; especially
with large lists this can be a win)

Cheers,

--Tim

[I V]

Re: printing out elements in list

On Mon, 08 May 2006 00:44:39 -0700, micklee74 wrote:[color=blue]
> i have a list with contents like this
> alist = ['>QWER' , 'askfhs', '>REWR' ,'sfsdf' , '>FGDG',
> 'sdfsdgffdgfdg' ]
>
> how can i "convert" this list into a dictionary such that
>
> dictionary = { '>QWER':'askfhs ' , '>REWR' : 'sfsdf' , '>FGDG',
> 'sdfsdgffdgfdg' }[/color]

This strikes me as a little bit voodish, but you could do:

dictionary = dict(zip(alist[::2], alist[1::2]))

[micklee74@hotmail.com]

Re: printing out elements in list

thanks for all your replies...I will go test them out..
I was wondering what does this mean alist[1::2]?
thanks

[Tim N. van der Leeuw]

Re: printing out elements in list

alist[::2] means taking a slice. You should look up slice-syntax in the
tutorials and reference manual.

in general,

alist[1:5] means: take list elements position 1 up to (excluding) 5.
(List indexing starts at position 0, so the first element in the list
is not included!)
alist[0:5] means: take list elements position 0 up to (excluding) 5; in
other words: the first 5 elements.
A shortcut for this is: alist[:5] -- omitting an index position means a
default of 'start' resp. 'end'.
So to take all elements from the 5th to the end of list, you write:
alist[4:] (remember that indexing starts at position 0, so 0 is your
first element, 4 is your 5th).

To take a slice that is the whole list, write: alist[:]

Slices discussed so far take all elements in the indicated range,
however you can specify a 'step' with your slices. Default step is 1,
but to skip every other element you write:
alist[::2]
Which takes all elements of your list, starting at position 0, adding 2
to the index each step, so next is item 2, then 4, etc, until end of
list.
Now we have all the 'even-numbered' elements in the list, to get the
'odd-numbered elements' write:
alist[1::2]

I hope this helps.


Cheers,

--Tim

[micklee74@hotmail.com]

Re: printing out elements in list

thanks for the detailed explaination... i know about basic lists
slicing..just havn't seen one with "steps" yet..
thanks again...clp rocks.