Question

I’m writing code so you can shift text two places along the alphabet: ‘ab cd’ should become ‘cd ef’. I’m using Python 2 and this is what I got so far:

def shifttext(shift):
    input=raw_input('Input text here: ')
    data = list(input)
    for i in data:
        data[i] = chr((ord(i) + shift) % 26)
        output = ''.join(data)
    return output
shifttext(3)

I get the following error:

File "level1.py", line 9, in <module>
    shifttext(3)
File "level1.py", line 5, in shifttext
    data[i] = chr((ord(i) + shift) % 26)
TypError: list indices must be integers, not str

So I have to change the letter to numbers somehow? But I thought I already did that?

Answer 1

Looks you’re doing cesar-cipher encryption, so you can try something like this:

strs = 'abcdefghijklmnopqrstuvwxyz'      # use a string like this, instead of ord() 
def shifttext(shift):
    inp = raw_input('Input text here: ')
    data = []
    for i in inp:                     # iterate over the text not some list
        if i.strip() and i in strs:                 # if the char is not a space ""  
            data.append(strs[(strs.index(i) + shift) % 26])    
        else:
            data.append(i)           # if space then simply append it to data
    output = ''.join(data)
    return output

output:

In [2]: shifttext(3)
Input text here: how are you?
Out[2]: 'krz duh brx?'

In [3]: shifttext(3)
Input text here: Fine.
Out[3]: 'Flqh.'

strs[(strs.index(i) + shift) % 26]: line above means find the index of the character i in strs and then add the shift value to it.Now, on the final value(index+shift) apply %26 to the get the shifted index. This shifted index when passed to strs[new_index] yields the desired shifted character.