replacing items in tuples

Question

I have to write a code that will switch the first item in a tuple with the last one, unless there is only one item. I understand in tuples this cannot be done, but it can be done in a list. So in my code I am changing the tuple to be a list. after running the code it should look like this:

    

>>>switchItems((6,4,8,3,7,9,4))
(4,4,8,3,7,9,6) 
>>>switchItems((“hi” , 23))
(23, “hi”) 
>>>switchItems((89,))
(89,)

My code doesn't do this. It returns a list in between and I don't really know how to make it work properly, this is my code:

    

switchItems(tuple):
    new = list(tuple)
    return new[-1],new [1:-2],new[0]

And it returns this:

    >>>switchItems((6,4,8,3,7,9,4))
        (4, [4, 8, 3, 7], 6)'

Answer 1

This is one way to fix your code.

def switchItems(tup):
    if len(tup) > 1:
        new = list(tup)
        new[0], new[-1] = new[-1], new[0]
        return tuple(new)
    return tup

Length check helps avoid possible errors and needles tuple to list to tuple conversion.

Now, let's talk a bit about your problems.

• The function switchItems was not properly defined. In Python you are supposed to use def (or lambda) to define a function, but I'm sure that is an artifact of copy-pasting.

• You shouldn't use argument names that shadow built-in names, i.e. don't use tuple as an argument name.

• According to PEP8 you should avoid using CamelCase to name functions in Python, e.g. switchItems should be switch_items. This is not enforced, but highly appreciated.

Answer 2

The length does not matter, you just have to swap the first and last elements:

def switch_items(t): # use lowercase  and underscores for function names
    t = list(t)
    t[0],t[-1] = t[-1],t[0]
    return tuple(t)

You would maybe want to catch an empty tuple though:

Or slice and check the len:

def switch_items(t):
    return  t[-1:] + t[1:-1] + t[0:1] if len(t) > 1 else t

Answer 3

If you just need a copy of switched tuple. (Certainly you won't get it in place)

def switchItems(t):
    if len(t) > 1:
        return tuple(t[-1] + list(t[1:-2]) + t[0])
    return t

Answer 4

You can do the following:

def switchItems(my_tuple): 
    l1 = list(my_tuple)  # Convert to a list
    if l1:  # check if not empty to prevent 'list index out of range' error 
        l1[0], l1[-1] = l1[-1], l1[0]  #swap first and last items

    return tuple(l1)

You pass the tuple to switchItems() function. The function converts the tuple to a list. It then swaps the first and last element using indices 0 and -1 if list obtained in previous step was not empty. This is done to prevent list index out of range error on accessing first and last element.