CODEWITHSUNDEEP
pythonfor-loopnested-lists
Jeremy
Jeremy

Reputation: 653

for loops and lists assignment

I've been given the assignment as follows:

Write a function called insert that takes 3 parameters, listA, listB and an index, then returns a copy of listA with the elements of listB inserted at the index. Your code should work with both strings and lists.

examples should look give this:

insert([1,2,3], ['a', 'b', 'c'], 3) should give [1, 2, 'a', 'b', 'c', 3]

AND:

insert('dog', 'cat', 1) should give 'dcatog'

I want to complete this first part both with and without loops. So far I have gotten:

def insert (listA, listB, index):
    return listA[0:index] + listB + listA[index:len(listA)]

and this works out correctly, giving the correct example shown above. I don't know how to do this with loops, though. I've been trying to use for loops as follows:

def insert (listA, listB, index):

    for nextchar in listA:
            if nextchar == index:
                listA.insert(index, listB)
        return listA

but that's not correct. It's the closest I've gotten though, giving 

[1, 2, ['a', 'b', 'c'], 3]

AND

'dog'

for the examples above.

but that's a nested list, yes? I don't want that. and the second example is completely wrong.

Upvotes: 0

Views: 184

Answers (2)

Grizz
Grizz

Reputation: 320

For the "dog" example, remember that strings in Python are immutable... that is, they can't be changed. So if you are trying to insert some characters into a string "dog", it won't be changed.

Strings don't have the "insert" method at all, so you will get an error in the "dog" example.

You will need to create a new string, and NOT use the insert method, if it's a string being passed in.

Upvotes: 1

beeftaco
beeftaco

Reputation: 63

Your example is a bit off I believe.

insert([1,2,3], ['a', 'b', 'c'], 3)

should in fact return 

[1, 2, 3, 'a', 'b', 'c']

Anyhow, here's my fix:

def insert (listA, listB, index):
    if index == len(listA):
        listA.extend(listB)
        return listA

    for i in range(len(listA)):
        print i
        if i == index:
            for j, b_elem in enumerate(listB):
                listA.insert(i+j, b_elem)
    return listA

A bug with your given code is that you are inserting a list into that index of listA, as opposed to inserting each element of listB STARTING from that index.

Upvotes: 0

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