CODEWITHSUNDEEP
python
Seth Johnson
Seth Johnson

Reputation: 15192

Creating a palindrome list with reverse()

I want to take a list [0,1,2] and turn it into [0,1,2,2,1,0]. Right now, I've got

r = list(mus)
r.reverse()
mus = mus + r

but it seems like there should be a better way. Can anyone come up with a good, pythonic one-liner?

Upvotes: 1

Views: 710

Answers (2)

Aaron
Aaron

Reputation: 1072

Just a few of the many ways to do this are:

  1. m = l + reversed(l)
  2. m = l + l[::-1]
  3. l.extend(reversed(l))
  4. l.extend(l[::-1])

The first two assign the output to a new list, and the second two update the list in place. If I was being clever, I would probably use 2 or 4, but if I wanted there to be no mistake about what I was doing, then I would opt for 1 or 3.

Hope this helps.

Edit: As pointed out in the comments, #1 doesn't work, as reversed returns an iterator. You could make it work by changing it to:

m = l + list(reversed(l))

But I can't recommend it. Go with 2 instead.

BTW, thanks for the correction and sorry for any confusion.

Upvotes: 2

Mike Graham
Mike Graham

Reputation: 76753

It looks like you might be in need of

mus.extend(reversed(mus))

Or if you simply need to iterate over this and not necessarily form the list, use

import itertools
for item in itertools.chain(mus, reversed(mus)):
    do_something...

Upvotes: 3

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