swap letters in a string in python

Question

I am trying to switch the first character in a string and move it to the end of the string. It needs to repeat the rotation a number of n times. For example, rotateLeft(hello,2)=llohe.

I tried doing

def rotateLeft(str,n):
    rotated=""
    rotated=str[n:]+str[:n]
    return rotated 

Is this right, and how would you do it if it remove the last character and move it to the front of the string?

Answer 1

You can shorten it to

def rotate(strg,n):
    return strg[n:] + strg[:n]

and simply use negative indices to rotate "to the right":

>>> rotate("hello", 2)
'llohe'
>>> rotate("hello", -1)
'ohell'
>>> rotate("hello", 1)
'elloh'
>>> rotate("hello", 4)
'ohell'
>>> rotate("hello", -3)
'llohe'
>>> rotate("hello", 6)  # same with -6: no change if n > len(strg)
'hello' 

If you want to keep rotating even after exceeding the length of the string, use

def rotate(strg,n):
    n = n % len(strg)
    return strg[n:] + strg[:n]

so you get

>>> rotate("hello", 1)
'elloh'
>>> rotate("hello", 6)
'elloh'