Create a slice using a tuple

Question

Is there any way in python to use a tuple as the indices for a slice? The following is not valid:

>>> a = range(20)
>>> b = (5, 12)   # my slice indices
>>> a[b]          # not valid
>>> a[slice(b)]   # not valid
>>> a[b[0]:b[1]] # is an awkward syntax
[5, 6, 7, 8, 9, 10, 11]
>>> b1, b2 = b
>>> a[b1:b2]      # looks a bit cleaner
[5, 6, 7, 8, 9, 10, 11]

It seems like a reasonably pythonic syntax so I am surprised that I can't do it.

score 44 · Accepted Answer · answered Aug 15 '11 at 21:58

You can use Python's *args syntax for this:

>>> a = range(20)
>>> b = (5, 12)
>>> a[slice(*b)]
[5, 6, 7, 8, 9, 10, 11]

Basically, you're telling Python to unpack the tuple b into individual elements and pass each of those elements to the slice() function as individual arguments.

score 13 · Answer 2 · edited Jun 10 '13 at 10:57

13

How about a[slice(*b)]?

Is that sufficiently pythonic?

edited Jun 10 '13 at 10:57

Eugene Yarmash

131,677
37
301
358

answered Aug 15 '11 at 21:57

Foon

5,830
11
38
41

I had completely forgotten about python's `*args` syntax. It would be more pythonic though if I could just write `a[*b]`. Of course this would conflict with multi-dimensional arrays so the ordinary slicing syntax is still better. Inclusion of the word slice is longer but probably far more clearly illustrates the purpose of the code. – Mike Aug 15 '11 at 22:19

score 4 · Answer 3 · answered Aug 15 '11 at 21:58

4

slice takes up to three arguments, but you are only giving it one with a tuple. What you need to do is have python unpack it, like so:

a[slice(*b)]

answered Aug 15 '11 at 21:58

Ethan Furman

57,917
18
142
218

score 2 · Answer 4 · answered Aug 15 '11 at 21:59

2

Only one tiny character is missing ;)

In [2]: a = range(20)

In [3]: b = (5, 12)

In [4]: a[slice(*b)]
Out[4]: [5, 6, 7, 8, 9, 10, 11

answered Aug 15 '11 at 21:59

Martin Thurau

7,428
7
40
77

Create a slice using a tuple

4 Answers4

Linked