MIT 6.00x - PSet 5 answers by jonrsharpe

ProblemSet5.py

from string import ascii_lowercase as lower, ascii_uppercase as upper, ascii_letters as both

# 1. Build a coder
def buildCoder(shift):
    return dict(zip(both, (lower[shift:] + lower[:shift] + upper[shift:] + upper[:shift])))

# 2. Apply the coder
def applyCoder(text, coder):
    return "".join([coder.get(letter, letter) for letter in text])

# 3. Apply a shift
def applyShift(text, shift):
    return applyCoder(text, buildCoder(shift))

# 4. Find the best shift for given text
def findBestShift(wordList, text):
    words = text.split(" ")
    for shift in range(26):
        coder = buildCoder(shift)
        if sum(isWord(wordList, applyCoder(word, coder)) for word in words) > len(words) / 2:
            return shift
    return False

# 5. Decrypt the provided story
def decryptStory():
    return applyShift(story, findBestShift(loadWords(), getStoryString()))

# 6. Recursively reverse a string
def reverseString(aStr):
    return aStr[-1] + reverseString(aStr[:-1]) if len(aStr) > 0 else ""

# 7. Determine whether a word is X-ian
def x_ian(x, word):
    if len(x) == 0:
        return True
    else:
        split = word.find(x[0])
        return False if split == -1 else x_ian(x[1:], word[split + 1:])

# 8. Add typewriter-style line breaks
def insertNewlines(text, lineLength):
    split = text.find(" ", lineLength - 1)
    if split == -1:
        return text
    else:
        return text[:split] + "\n" + insertNewlines(text[split:], lineLength)