重新排列列表中的字母

Question

This may be a bit confusing to read but what I would like to do is take any string and rearrange the letters based on an input from the user of the program. So for example, line = "Romeo and Juliet", key=3. The encoded line would start with line[0] R, then move 3 characters down to E, then A, then a SPACE. Then once i reach the end of the list it would circle back and start with line[1], add 3, and so on until all the characters have been used. So the end result would be "Rea ltoonJim due". I'm assuming this will use a loop and that's the part I'm stuck on. This is my current code:

key = int(input("Enter the key: "))
sent = input("Enter a sentence: ")
print()# for turnin
print()

print("With a key of:",key)
print("Original sentence:",sent)
print()

split = list(sent)

for i in range(len(split)):
    print(split[0+i*key])

So I have the list set up, and this gives me the first few letters that I need but I get an error: IndexError: list index out of range.

So once it reaches the final character, how would i get it to loop back to split[1] and continue through?

Answer 1

You could do split[(i*key) % len(split)] to rotate around the list. Look up more on modulo .

Answer 2

String slicing can take a "skip" factor, so:

>>> s = 'Romeo and Juliet'
>>> s[0::3] # every 3rd letter starting from 0
'Rea lt'
>>> s[1::3] # every 3rd letter starting from 1
'oonJi'

Put that in a loop and join them together:

>>> ''.join(s[i::3] for i in range(3))
'Rea ltoonJim due'

As a general function:

>>> def rearrange(s,skip):
...     return ''.join(s[i::skip] for i in range(skip))
... 
>>> rearrange(s,3)
'Rea ltoonJim due'
>>> rearrange(s,5)
'R Jtoaumnledio e'