2

I have tried the Sequence Generator like Lambda, List comprehension and others but it seems that I am not able to get what I really want. My final goal is to print sequence of words from a string like string[1:3]

What I am looking for :

a = [0,13,26,39]
b = [12,25,38,51]

str = 'If you are done with the file, move to the command area across from the file name in the RL screen and type'

read = str.split()

read[0:12]
['If', 'you', 'are', 'done', 'with', 'the', 'file,', 'move', 'to', 'the', 'command', 'area']
read[13:25]
['from', 'the', 'file', 'name', 'in', 'the', 'RL', 'screen', 'and', 'type']
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2
  • 2
    Well, what's the question? Commented Jun 21, 2013 at 16:57
  • If I may ask, in what context did you find such a problem? Commented Jun 21, 2013 at 18:29

4 Answers 4

Reset to default
5

Use zip:

>>> a = [0,13,26,39]
>>> b = [12,25,38,51]
>>> strs = 'If you are done with the file, move to the command area across from the file name in the RL screen and type'
>>> spl = strs.split()
>>> for x,y in zip(a,b):
...     print spl[x:y]
...     
['If', 'you', 'are', 'done', 'with', 'the', 'file,', 'move', 'to', 'the', 'command', 'area']
['from', 'the', 'file', 'name', 'in', 'the', 'RL', 'screen', 'and', 'type']
[]
[]

zip returns list of tuples, where each tuple contains items on the same index from the iterables passed to it:

>>> zip(a,b)
[(0, 12), (13, 25), (26, 38), (39, 51)]

Use itertools.izip if you want memory efficient solution, as it returns an iterator.

You can use str.join if you want to create a string from that sliced list:

for x,y in zip(a,b):
    print " ".join(spl[x:y])
...     
If you are done with the file, move to the command area
from the file name in the RL screen and type

Update: Creating a and b:

>>> n = 5
>>> a = range(0, 13*n, 13)
>>> b = [ x + 12 for x in a]
>>> a
[0, 13, 26, 39, 52]
>>> b
[12, 25, 38, 51, 64]
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1 Comment

And how can I create the list a and b. These are sequences in which N+1 number is 13 more in case of a and b. Also b[0] = a[0] + 12
3

Do you mean:

>>> [read[i:j] for i, j in zip(a,b)]
[['If', 'you', 'are', 'done', 'with', 'the', 'file,', 'move', 'to', 'the', 
'command',    'area'], ['from', 'the', 'file', 'name', 'in', 'the', 'RL',
'screen', 'and', 'type'], [], []]

or

>>> ' '.join[read[i:j] for i, j in zip(a,b)][0])
'If you are done with the file, move to the command area'

>>> ' '.join[read[i:j] for i, j in zip(a,b)][1])
'from the file name in the RL screen and type'
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Comments

2 
a = [0,13,26,39]
b = [12,25,38,51]
str = 'If you are done with the file, move to the command area across from the file name  in the RL screen and type'

read = str.split()
extra_lists = [read[start:end] for start,end in zip(a,b)]
print extra_lists
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Comments

1

You mentioned a lambda, so:

 f = lambda s, i, j: s.split()[i:j]
 >>> f("hello world how are you",0,2)
 ['hello', 'world']

Seems like you're doing the slice indices in two lists, might I suggest a dictionary or a list of tuples?

str = 'If you are done with the file, move to the command area across from the file name in the RL screen and type'
slices = [(0, 13), (12, 25)]
dslices = {0:13, 12:25}
for pair in slices:
    print f(str, pair[0], pair[1])
for key in dslices:
    print f(str, key, dislikes[key])

I'm not a fan of using zip when you have the option of just formatting your data better.

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