One Time Pad in Python
Here are some of your functions translated to be more pythonic:

Context managers mean never having to say your closed():

We can recast thse 2 functions (including fixing the bug of not closing the files):

def read(name):
    inFile = open(name, 'r')
    content = inFile.read()
    content = list(content.strip())
    return content

def write(name, nList):
    outFile = open(name, 'w')
    cList = convertToChar(nList)
    outFile.write(''.join(cList))


to:

def read(name):
    with open(name, 'r') as f:
        return f.read().strip()

def write(name, n_list):
    with open(name, 'w') as f:
        f.write(''.join(convertToChar(n_list)))


big key here is using context managers to automatically close the file, and not bothering to assign intermediate results to a variable.

List comprehensions can save a lot of looping boilerplate:

We will trim down:

def gen(keylen):
    i = 0
    key = []
    while i &lt; keylen:
        k = random.SystemRandom()
        k = k.choice(string.printable)
        key.append(k)
        i += 1
    key = convertToNum(key)
    write("key.txt", key)
    return key

def convertToNum(charList):
    numList = []
    i = 0
    for i in charList:
        numList.append(ord(i))
    return numList

def convertToChar(numList):
    charList = []
    i = 0
    for i in numList:
        charList.append(chr(i))
    return charList


To:

def gen(keylen):
    key = convertToNum([random.SystemRandom().choice(string.printable)
                        for k in range(keylen)])
    write("key.txt", key)
    return key

def convertToNum(charList):
    return [ord(i) for i in charList]

def convertToChar(numList):
    return [chr(i) for i in numList]


All three of these functions now make use of list comprehensions to remove 75% of the lines of code.

NOTE

I did not test these changes they were just typed out in the editor.