Cipher/decipher program

[slurpz]

I'm trying to make a simple program that will convert to and from a cipher that's already set.

foo = 'a = hz\nb = ye\nc = uo\nd = pd\ne = qi\nf = jy\ng = ru\nh = sw\ni = ln\nj = ae\nk = na\nl = rt\nm = wu\nn = is\no = nd\np = hw\nq = op\nr = kb\ns = vf\nt = fc\nu = xr\nv = ex\nw = mn\nx = gb\ny = bu\nz = ie\n. =  *right wing slash* \n, =  *hand wave* \n" =  *hand curve* \n! =  *double hand jerk* \n? =  *wing wave* \n... =  *squiggly hand motion* '
repl={}
reverse_repl={}
import sys
#Generate replacement tables
for str in foo.split("\n"):
    parts=str.split(" = ")
    repl[parts[0]]=parts[1]
    repl[parts[0].lower()]=parts[1]
    reverse_repl[parts[1]]=parts[0]
def encipher():
    outstr = ''
    instr = sys.stdin.readline()
    i = 0
    for i in range(len(instr)):
        c = instr[i]
        if (instr[i:i+3]=='...'):
            outstr+=repl['...']
            i+=3
        else:
            if (c in repl):
                outstr+=repl[c]
                i+=1
            else:
                outstr+=c
                i+=1
    print outstr
def decipher():
    outstr = ''
    instr = sys.stdin.readline()
    instr=instr[:-1]
    i = 0
    c = instr[i]
    while (i<len(instr)):
            if (instr[i:i+2]):
                outstr+=reverse_repl[instr[i:i+2]]
                i+=2
            else:
                outstr+=c
                i+=1
    print outstr
if (sys.argv[1]=="-e"):
    encipher()
else:
    decipher()
raw_input('press Return to end program>')

Couple of things I couldn't get working:

1. I couldn't separate the '...' from the '.' The '...' will give the correct equivalent from the list when enciphering, but will also follow it with 2 instances of '.'
2. For deciphering, it works up until it goes up against a character that's not in "foo" like 123 or a space.

Thanks for your help in advance.

[bvdet]

It appears that you want to replace each character with a unique 2 character string with a special exception for "...". I don't understand what *squiggly hand motion* is, but I'll assume that it is 2 characters. If a character is not in repl, double it so we be consistent.

Your code:

    for i in range(len(instr)):
        c = instr[i]
        if (instr[i:i+3]=='...'):
            outstr+=repl['...']
            i+=3
        else:
            if (c in repl):
                outstr+=repl[c]
                i+=1
            else:
                outstr+=c
                i+=1

Variable i is updated each iteration. If you assign i in the body of the loop, you will lose the assignment.
Try the following instead:

    while i < len(instr):
        c = instr[i]
        if instr[i:i+3] == '...':
            outstr += repl['...']
            i+=3
        elif c in repl:
            outstr += repl[c]
            i+=1
        else:
            outstr += c*2
            i+=1

To get the code to work, I replaced your code:

    while (i<len(instr)):
            if (instr[i:i+2]):
                outstr+=reverse_repl[instr[i:i+2]]
                i+=2
            else:
                outstr+=c
                i+=1

with the following code:

    while i<len(instr):
        if reverse_repl.has_key(instr[i:i+2]):
            outstr += reverse_repl[instr[i:i+2]]
        else:
            outstr += instr[i][0]
        i+=2

There were several places in your code where parentheses were not required. Avoid using str as a variable name, because the built-in function str() will be masked.
HTH --BV

[slurpz]

Thanks for the quick reply. I actually worked a bit on my code while I waited so my code looks pretty similar to yours. My code looks like this right now:

foo = 'a = hz\nb = ye\n... =  *squiggly hand motion* \nc = uo\nd = pd\ne = qi\nf = jy\ng = ru\nh = sw\nI = xegy\ni = ln\nj = ae\nk = na\nl = rt\nm = wu\nn = is\no = nd\np = hw\nq = op\nr = kb\ns = vf\nt = fc\nu = xr\nv = ex\nw = mn\nx = gb\ny = bu\nz = ie\n. =  *right wing slash* \n, =  *hand wave* \n" =  *hand curve* \n! =  *double hand jerk* \n? =  *wing wave* '
repl={}
reverse_repl={}
import sys
#Generate replacement tables
for str in foo.split("\n"):
    parts=str.split(" = ")
    repl[parts[0]]=parts[1]
    repl[parts[0].lower()]=parts[1]
    reverse_repl[parts[1]]=parts[0]
def encipher():
    outstr = ''
    instr = sys.stdin.readline()
    i = 0
    n = len(instr)
    while i < n:
        c = instr[i] 
        if instr[i:i+3] == '...': 
            outstr += repl['...'] 
            i+=3 
        elif c in repl: 
            outstr += repl[c] 
            i+=1 
        else: 
            outstr += c
            i+=1
    print outstr
def decipher():
    outstr = ''
    instr = sys.stdin.readline()
    i = 0
    n = len(instr)
    while i < n:
        if instr[i:i+2] in reverse_repl:
            outstr+=reverse_repl[instr[i:i+2]]
            i+=2
        else:
            outstr+=instr[i]
            i+=1
    print outstr
if (sys.argv[1]=="-e"):
    encipher()
else:
    decipher()
raw_input('press Return to end program>')

Enciphering works perfectly (that "..." fix was great), but now with deciphering, there are a couple values that take up more than 2 letters.

These include:
*right wing slash* = .
*hand wave* = ,
*hand curve* = "
*double hand jerk* = !
*wing wave* = ?
*squiggly hand motion* = ...
xegy = I

Is there a more efficient way than searching for each one individually? (Maybe from an array or something?)

[bvdet]

You should consider processing these special cases separately. Example:

dd = {'*right wing slash*': '.',
      '*hand wave*': ',',
      '*hand curve*': '"',
      '*double hand jerk*': '!',
      '*wing wave*': '?',
      '*squiggly hand motion*': '...',
      'xegy': 'I'}
 
def fix_str(s):
    for key in dd:
        s = s.replace(key, dd[key])
    return s

>>> print fix_str("*right wing slash**hand wave**hand curve*")
.,"
>>> 

[MojaveKid]

2 digit encryption...the closest thing to this will be the BIFID cipher

try reading this: http://en.wikipedia.org/wiki/Bifid_cipher

it should give you a good idea on the algorithm