Take list foo
foo = [5, 6, 7, 8, 9, 10, 11, 12]
How can I reverse only the elements of indices x to y within the list?
For example:
x = 1
y = 5
# reverse foo[x:y]
foo = [5, 9, 8, 7, 6, 10, 11, 12]
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Slice it out, reverse it, and concatenate everything back together.Jonathon Reinhart– Jonathon Reinhart2015-03-29 14:41:50 +00:00Commented Mar 29, 2015 at 14:41
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3 Answers
Python allows you to assign to slices
Slicings may be used as expressions or as targets in assignment or del statements
thus it's possible to do everything on one line:
foo[x:y] = foo[y-1:x-1:-1]
Note thatfoo[y-1:x-1:-1] has the same meaning as foo[x:y][::-1].
1 Comment
Alessandro Teruzzi
it doesn't seems to work when x is pointing the index 0
It's as simple as:
foo[x:y] = foo[y - 1:x - 1:-1]
For example:
>>> foo = [5, 6, 7, 8, 9, 10, 11, 12]
>>> foo[1:5] = foo[4:0:-1]
>>> foo
[5, 9, 8, 7, 6, 10, 11, 12]
1 Comment
chambln
can I get that in terms of x and y?
def reverse(l, x, y):
l[x:y+1] = l[y:x-1:-1]
foo = [5, 6, 7, 8, 9, 10, 11, 12]
x = 1
y = 4
reverse(foo, x, y)
print(foo) # [5, 9, 8, 7, 6, 10, 11, 12]
