在不使用 insert() 的情况下将项目插入 Python 列表

Question

How do you add an item to a specific position on a list. When you have an empty list and want to add 'z' to the 3rd position using insert() only insert it at the last position like,

l.insert(3,'z')
l
['z']

I want the output to be

[None, None, None, 'z']

or

['','','','z']

Answer 1

Assuming you want to have it in the Nth index:

l = l[:N] + ['z'] + l[N:]

If you start with an empty list and want it to have Nones at the start and end of array, maybe this will help you (N is the number of None items you want):

l = [None] * N
l = l[:N] + ['z'] + l[N:]

Answer 2

Try this method using a list comprehension -

n = 5
s = 'z'

out = [None if i!=n-1 else s for i in range(n)]
print(out)

[None, None, None, None, 'z']

If you want to insert the string somewhere in the middle, then a more general way is to define m and n separately where n is length of the list and m is the position -

n = 5
m = 3
s = 'z'

out = [None if i!=m-1 else s for i in range(n)]
print(out)

[None, None, 'z', None, None]