Python returns first and last item of a sequence exchanged

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I need to create a function to slice a sequence in order that first and last item is exchanged and the middle stays in the middle. It needs to be able to handle string/list/tuples. I am having trouble with typeerrors - cant add list + int.

This:

def exchange_first_last(seq):
    """This returns the first and last item of a sequence exchanged"""
    first = seq[-1]
    mid = seq[1:-1]
    last = seq[0]
    return print(first+mid+last)

produces

(5, [2, 3, 4], 1)

But I don't want a list inside a tuple, just one flowing sequence.

(5,2,3,4,1,)

Any hints/suggestions welcome. The idea is to slice properly in order to handle different object types.

Try this:

def exchange_first_last(seq):
    """This returns the first and last item of a sequence exchanged"""
    first = seq[-1:]
    mid = seq[1:-1]
    last = seq[:1]
    return print(first+mid+last)

Python program to interchange first and last elements in a list , Given a list, write a Python program to swap first and last element of the list. Examples: return newList Now, the First and last values in that list are swapped. Python | Get first and last elements of a list Sometimes, there might be a need to get the range between which a number lies in the list, for such applications we require to get the first and last element of the list.

Change your code a little, notice the square brackets:

def exchange_first_last(seq):
    """This returns the first and last item of a sequence exchanged"""
    first = seq[-1]
    mid = seq[1:-1]
    last = seq[0]
    return print([first]+mid+[last])

Note it actually gives you a list, i.e. [5,2,3,4,1], not a tuple (5,2,3,4,1).

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You can use list.extend():

def exchange_first_last(seq):
    """This returns the first and last item of a sequence exchanged"""
    first = seq[-1]
    mid = seq[1:-1]
    last = seq[0]
    merged = []
    merged.extend(first)
    merged.extend(mid)
    merged.extend(last)
    return merged

Comp-Computer Science-TB-12, Python provides a sort() method for sorting a list, it cannot be used with an array or can be applied to data stored in a mutable sequence such as an array or list. The first and second elements are compared and swapped if out of order. until the last two elements of the array are compared and swapped if out of order. Write some functions that take a sequence as an argument, and return a copy of that sequence: with the first and last items exchanged. with every other item removed. with the first 4 and the last 4 items removed, and then every other item in the remaining sequence. with the elements reversed (just with slicing).

You could just swap the elements

def swap(l):
     temp = l[0]
     l[0] = l[-1]
     l[-1] = temp
     return l

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Heap's algorithm, Heap's algorithm generates all possible permutations of n objects. It was first proposed by B. R. The sequence of permutations of n objects generated by Heap's algorithm is the a rule is needed at each iteration to select which will be exchanged with the last. is odd, the final element is always exchanged with the first. The only difference is that range returns a Python list object and xrange returns an xrange object. It means that xrange doesn’t actually generate a static list at run-time like range does. It creates the values as you need them with a special technique called yielding.

Comments
  • What is seq value? As I don't understand what you want to achieve.
  • Extract the fist and last elements as slices too; first = seq[-1:] and last = seq[:1]. Then they'll have the same type as seq, and addition will work fine.
  • Why do you return the return value of print, which is None?
  • I just did this myself and it worked, came back here and saw what people said and here you are! Thanks much!
  • type(seq)([first]+mid+[last]) to make it a tuple when necesarry although I think a if is just much better
  • This will not work with immutables like strings and tuples.
  • Didnt realize it was tuples