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?
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'
The only problem with the code you have posted is the fact that you're trying to use "str" as a name for a string. This is the name of a built in function in Python, and that's why you're getting errors. See more: http://docs.python.org/library/functions.html#str You cannot use that as a name for something.
Changing the name of the string you pass rotateLeft will solve your problem.
def rotateLeft(string,n):
rotated=""
rotated=string[n:]+string[:n]
return rotated
I know this is old, but you can use collections.deque:
from collections import deque
s = 'Impending doom approaches!'
d = deque(s)
d.rotate(11)
print(''.join(d))
>>> approaches!Impending doom
d.rotate(-21)
print(''.join(d))
>>> doom approaches!Impending
