I am currently doing an assignment that encrypts text by using rot 13, but some of my text wont register.
# cgi is to escape html
# import cgi
def rot13(s):
#string encrypted
scrypt=''
alph='abcdefghijklmonpqrstuvwxyz'
for c in s:
# check if char is in alphabet
if c.lower() in alph:
#find c in alph and return its place
i = alph.find(c.lower())
#encrypt char = c incremented by 13
ccrypt = alph[ i+13 : i+14 ]
#add encrypted char to string
if c==c.lower():
scrypt+=ccrypt
if c==c.upper():
scrypt+=ccrypt.upper()
#dont encrypt special chars or spaces
else:
scrypt+=c
return scrypt
# return cgi.escape(scrypt, quote = True)
given_string = 'Rot13 Test'
print rot13(given_string)
13 r
[Finished in 0.0s]
First thing that may have caused you some problems - your string list has the n and the o switched, so you'll want to adjust that :) As for the algorithm, when you run:
ccrypt = alph[ i+13 : i+14 ]
Think of what happens when you get 25 back from the first iteration (for z). You are now looking for the index position alph[38:39] (side note: you can actually just say alph[38]), which is far past the bounds of the 26-character string, which will return '':
In [1]: s = 'abcde'
In [2]: s[2]
Out[2]: 'c'
In [3]: s[2:3]
Out[3]: 'c'
In [4]: s[49:50]
Out[4]: ''
As for how to fix it, there are a number of interesting methods. Your code functions just fine with a few modifications. One thing you could do is create a mapping of characters that are already 'rotated' 13 positions:
alph = 'abcdefghijklmnopqrstuvwxyz'
coded = 'nopqrstuvwxyzabcdefghijklm'
All we did here is split the original list into halves of 13 and then swap them - we now know that if we take a letter like a and get its position (0), the same position in the coded list will be the rot13 value. As this is for an assignment I won't spell out how to do it, but see if that gets you on the right track (and @Makoto's suggestion is a perfect way to check your results).