Python List indexing multiple ranges

Question

Sorry if this has already been asked, I couldn't find it anywhere. Basically how do I get 2 separate ranges within a list in Python.

If I want the 1st, 2nd, 5th and 6th elements of a list I know I can do this,

l = range(0,15)
l[1:3]+l[5:7]

but this assumes that l is easy to write. However I am scrapping something from a webpage using BeautifulSoup4, so I'm using soup.find_all (which gives me a list), so I can't simply write out 2 lists, l and concatenate them.

I want an answer that is something like

l = range(0,15)
l[1:3,5:7]

(but of course without the error) :)

what is wrong with l[1:3]+l[5:7]?

Padraic Cunningham
– Padraic Cunningham

2015-04-21 20:23:13 +00:00
Commented Apr 21, 2015 at 20:23 — Padraic Cunningham
– Padraic Cunningham, Commented Apr 21, 2015 at 20:23

Mark Tolonen · Accepted Answer · 2015-04-21 20:23:13Z

3

This might be what you want. itemgetter creates a function that retrieves the listed indices:

>>> import operator
>>> snip = operator.itemgetter(1,2,5,6)
>>> snip(range(15))
(1, 2, 5, 6)
>>> snip('abcdefg')
('b', 'c', 'f', 'g')
>>> snip([1,2,3,4,5,6,7,8])
(2, 3, 6, 7)

answered Apr 21, 2015 at 20:23

Mark Tolonen

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rickcnagy · Accepted Answer · 2015-04-21 20:28:12Z

2

I would do this with a function:

def multi_range(l, *args):
    output = []
    for indices in args:
        output += l[indices[0]:indices[1]]
    return output

So the first argument would be the list, and the rest of the parameters are tuples with the indices you're looking to pull. It would work fine with a long list name:

long_list_name = range(0, 15)
print multi_range(long_list_name, (1, 3), (5, 7))
>>> [1, 2, 5, 6]

answered Apr 21, 2015 at 20:28

rickcnagy

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Padraic Cunningham · Accepted Answer · 2015-04-21 20:27:00Z

1

l = range(0, 15)
print([l[i] for i in [1,2, 5,6]])

Not sure why you think l[1:3]+l[5:7] is hard, find_all returns a normal python list like any other.

Or using map:

l = range(0, 15)
print(list(map(l.__getitem__,(1,2,5,6))))

edited Apr 21, 2015 at 20:27

answered Apr 21, 2015 at 20:21

Padraic Cunningham

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anon · Accepted Answer · 2015-04-21 20:25:09Z

-1

Is this OK?

indices = [1, 2, 5, 6]
selected = [l[i] for i in indices]

answered Apr 21, 2015 at 20:25

anon

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