Deciphering Text From Research Paper

estherDuflo.py

from string import *

# create decipher dictionary
l = letters[:26]
decipher = "".join([l[(i+3)%26] for i in range(len(l))])
decipher = dict(zip(decipher,l))

# open and read encrypted text
filename = 'estherDuflo.txt'
f = open(filename, 'rw')
lines = f.readlines()
lines = [l[:-1] for l in lines]
# use first 1475 lines only
newlines = lines[:1475]

# apply decryption on those 1475 lines
decipheredLines = []
for line in newlines:
    x = line.lower()
    s = []
    for letter in x:
        if letter in letters:
            s.append(decipher[letter])
        else:
            s.append(letter)
    s.append('\n')
    decipheredLines.append(''.join(s))

# write deciphered text to new text file
decipheredFile = 'estherDufloDeciphered.txt'
df = open(decipheredFile, 'w')
for line in decipheredLines:
    df.write("%s" % line)

# close both text files
f.close()
df.close()