CODEWITHSUNDEEP
pythontext
PlateArmor
PlateArmor

Reputation: 25

Program that Encrypts and Decrypts a text file

My sample text file is: 'abcd abcd abcd'

The program has a dictionary with symbols dedicated for each letter. The objective is to create a new file with the files message encrypted.

Program 'works'. By this I mean that it only converts abc. Since theres no d in the dictionary then it raises an error. I removed the d and tried again, but this raises another error called: KeyError: ' '

How can I make my program detect spaces, and write the letter even if theres no symbol for it?

def main():
    ecrypt = {'a':'%', 'b':'&', 'c':'/'}
    input_file = open('efile.txt', 'r')
    output_file = open('newefile.txt', 'w')
    line = input_file.readline()
    for letter in line:
        if letter in line:
            output_file.write(ecrypt[letter])            

main()

Upvotes: 2

Views: 287

Answers (2)

Kasravnd
Kasravnd

Reputation: 107287

You can use a try-except for handle the KeyError but as a more pythonic way you can use str.translate() function that is actually for this aim :

>>> from string import maketrans
>>> i='abc'
>>> o='%&/'
>>> trantab = maketrans(i, o)

>>> print 'abcd abcd abcd'.translate(trantab)
%&/d %&/d %&/d

and for translate the file and write in another file :

from string import maketrans
i='abc'
o='%&/'
trantab = maketrans(i, o)
with open('efile.txt', 'r') as infile,open('newefile.txt', 'w') as out :
    out.write(infile.read().translate(trantab))

Upvotes: 5

JAL
JAL

Reputation: 21563

You're trying to access ecrypt['d'] which doesn't exist. With this current code, you'd need to make sure every character (not just letter, punctuation... Spaces...) is in the ecrypt dict.

I suggest adding an exception. See https://docs.python.org/2/tutorial/errors.html The 'if letter in line' is superfluous.

for letter in line:
        try:
             output_file.write(ecrypt[letter])           
        except KeyError:
             output_file.write(letter)

Or, test that the letter exists first.

for letter in line:
    cipher_letter=ecrypt[letter] if letter in ecrypt else letter       
    output_file.write(cipher_letter)

Upvotes: 3

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