Python - Position of last character in sequence using similar method to one here

Question

def PositionLast(x,s):
    position = -1
    for i in s:
        position +=1
        if i == x:
            return position

Is what I have so far - just returns the first. Is there a way using similar means to return the last ? Thanks in advance

Answer 1

Seems that you want to return the last position of a character in your string.For that aim you can traverse your string from end to start :

def PositionLast(x,s):
    length=len(s)
    position = -1
    for i in s[::-1]:
        position +=1
    if i == x:
        return length-position 

But as a more pythonic way you can use enumerate and a generator expression within next function :

def PositionLast(x,s):
    return next(i for i,j in enumerate(s)[::-1] if j==x)

If you don't want to reverse the string you can use a deque object with max length one to preserve the positions, thus at the end it will preserver the last index :

from dollections import deque
def PositionLast(x,s,d=deque(maxlen=1)):
    position = -1
    for i in s:
        position +=1
    if i == x:
        d.append(position)
    return d.pop()

Answer 2

Is it just me or this looks like a CS assignment?

Anyway, one way is to iterate through the string in inverse order and use your code:

def PositionLast(x,s):
    position = -1
    for i in reversed(s):
        position +=1
    if i == x
        return position

There are of course many other ways to do this, and if this is really an assignment you should work a bit on it and figure them out.

Answer 3

You can use this:

def PositionLast(x,s):
  return len(x) - x[::-1].index(s) - 1

which basically reverses the array, looks for the first index, then finds the position in the original list.