[SOLVED] python scripting question

nickygencs17 · 05-06-2014, 11:19 AM

I need some help with rot 13 script that encrypts and decrypts, it can only import sys and not using maketrans or lamda but using the key

Code:

key = {'a':'n', 'b':'o', 'c':'p', 'd':'q', 'e':'r', 'f':'s', 'g':'t', 'h':'u',
       'i':'v', 'j':'w', 'k':'x', 'l':'y', 'm':'z', 'n':'a', 'o':'b', 'p':'c',
       'q':'d', 'r':'e', 's':'f', 't':'g', 'u':'h', 'v':'i', 'w':'j', 'x':'k',
       'y':'l', 'z':'m', 'A':'N', 'B':'O', 'C':'P', 'D':'Q', 'E':'R', 'F':'S',
       'G':'T', 'H':'U', 'I':'V', 'J':'W', 'K':'X', 'L':'Y', 'M':'Z', 'N':'A',
       'O':'B', 'P':'C', 'Q':'D', 'R':'E', 'S':'F', 'T':'G', 'U':'H', 'V':'I',
       'W':'J', 'X':'K', 'Y':'L', 'Z':'M'}

what i have so far is

Code:

#!/usr/bin/python
import sy





key = {'a':'n', 'b':'o', 'c':'p', 'd':'q', 'e':'r', 'f':'s', 'g':'t', 'h':'u',
       'i':'v', 'j':'w', 'k':'x', 'l':'y', 'm':'z', 'n':'a', 'o':'b', 'p':'c',
       'q':'d', 'r':'e', 's':'f', 't':'g', 'u':'h', 'v':'i', 'w':'j', 'x':'k',
       'y':'l', 'z':'m', 'A':'N', 'B':'O', 'C':'P', 'D':'Q', 'E':'R', 'F':'S',
       'G':'T', 'H':'U', 'I':'V', 'J':'W', 'K':'X', 'L':'Y', 'M':'Z', 'N':'A',
       'O':'B', 'P':'C', 'Q':'D', 'R':'E', 'S':'F', 'T':'G', 'U':'H', 'V':'I',
       'W':'J', 'X':'K', 'Y':'L', 'Z':'M'}




if(len(sys.argv)==3):
        if (sys.argv[1] == "d"):
                for c in sys.argv[1]:
                        print (key['c'])




else
        print "Only filename and two arguments please"
        return
~                                                                                                                                                                                    
~                                                                                                                                                                                    
~

I've only just learned python and its very confusing i appreciate all the help and the constructive criticism thank you very much - nick

sundialsvcs · 05-06-2014, 02:06 PM

And you're getting a row of the letter "p" as your result, aren't you?

Ask your instructor for further help with your homework, but, before you do, consider "literally" what you are right now asking the computer to do. You can quote me on that, in fact.

mina86 · 05-06-2014, 05:17 PM

The usage of your script is actually unclear. What are the two arguments the script accept? Anyway, to open a file, you need to use open function.

nickygencs17 · 05-06-2014, 11:18 PM

no sundialsvcs that was never the problem c is a character in the passed string and mina86 the arguments were d for decoding and e for encoding and the message to be en/de coded well anyway i worked on it and solved it myself here is the finished product but thanks for the help

Code:

#!/usr/bin/python
#Nicholas Genco
import sys #importing sys libary
stringname = "" #setting stringname to empty string 

key = {'a':'n', 'b':'o', 'c':'p', 'd':'q', 'e':'r', 'f':'s', 'g':'t', 'h':'u',
       'i':'v', 'j':'w', 'k':'x', 'l':'y', 'm':'z', 'n':'a', 'o':'b', 'p':'c',
       'q':'d', 'r':'e', 's':'f', 't':'g', 'u':'h', 'v':'i', 'w':'j', 'x':'k',
       'y':'l', 'z':'m', 'A':'N', 'B':'O', 'C':'P', 'D':'Q', 'E':'R', 'F':'S',
       'G':'T', 'H':'U', 'I':'V', 'J':'W', 'K':'X', 'L':'Y', 'M':'Z', 'N':'A',
       'O':'B', 'P':'C', 'Q':'D', 'R':'E', 'S':'F', 'T':'G', 'U':'H', 'V':'I',
       'W':'J', 'X':'K', 'Y':'L', 'Z':'M'}
#making a dict called key

dkey=dict(zip(key.values(),key))
#reversing key

lenggthh=len(sys.argv)#length of sys.argv set to int 
if (lenggthh == 3): #testing if length is greater then e
        if (sys.argv[1] == "e" or sys.argv[1] == "E"): #testing if second argument is e
                for c in sys.argv[2]: #encoding message 
                        if c in key: #if c is in key
                                stringname=stringname+key[c] #add key of c to emptystring 
                        else: #if stringname is special character
                                stringname=stringname+c #add special character 
        elif (sys.argv[1] == "d" or sys.argv[1] == "D"): #testing if second argument is d
                for f in sys.argv[2]: #decoding message         
                        if f in dkey: #testing if f is in dkey
                                stringname=stringname+dkey[f] #adding key of f into emptystring
                        else: #testing for special characters
                                stringname=stringname+f#adding special character
        else:#else second argument is not d or e
                print "ERROR: SECOND ARGUMENT IS NOT D/d or E/E"
                sys.exit(12)#system exit 
else:#else to arguments
        print " MUST HAVE THREE ARGUMENTS"
        sys.exit(9)#system exit
print stringname#printing stringname
sys.exit(0)#system exit 0
~

grail · 05-07-2014, 07:43 AM

Well good to see you found a solution, although I would say the initial script was riddled with errors.

As for your new solution, my one gripe would be the ineffectual error message you return when someone enters the wrong number of arguments:

Code:

print " MUST HAVE THREE ARGUMENTS"

Whilst the novice user now realises that 3 arguments are required, they are given no indication as to what they might be or if there is any desired order.
Might be something to think about

rscudder · 05-07-2014, 07:58 AM

If that works for you, good. The comments aren't very helpful though. They should explain what is going on but is not obvious.

This line is a great example of poor use of a comments.

if c in key: #if c is in key

mina86 · 05-07-2014, 09:31 AM

Ah, now I see. I thought the script was supposed to operate on a file and not on the second argument.

Few notes on your code (this is in addition to what grail and rscudder have said):
1. You do not need parenthesis around if condition.
2. “dkey=dict(zip(key.values(),key))” -- I would fear that construct. I don't know if there are any guarantees that you'll get values and keys in the same order. I'd do “dkey = dict((b, a) for a, b in key.items())”.
2a. On that topic, when the string is being encoded, dkey is never used, and this computation is not needed. Perhaps it would be better to compute dkey only when it's needed?
3. You are aware that in rot-13 encoding and decoding is the same thing, right?
4. Check out dictionary's get method, e.g. “result += key.get(next_char, next_char)” allows you to get rid of the “if next_char in key” condition.
5. Instead of comparing to “d” and then to “D”, use “lower” method of a string.
6. Did you notice how encoding and decoding is the same code except one uses key and the other uses dkey dictionary? You should move that common code to a function and pass the string to operate on and the key as arguments.
7. You do not need sys.exit(0) at the end.
8. If you handle “len(sys.argv) != 3” case first, you can put the whole majority of the code out of if body. This means you save one indention level. This will make the code look less complex.