Crappy modified twitter archive markov

#!/usr/bin/env python
import random, re, sys, csv, time
from collections import deque

order = 2
source = "tweets.csv" # input text
prefix = deque([" "] * order) # current prefix
suffixes = {} # a dictionary maps prefix to a list of following strings

def add(s):
    key = '@!@'.join(prefix)
    if key in suffixes:
        suffixes[key].append(s)
    else:
        suffixes[key] = [ s ]
    prefix.popleft()
    prefix.append(s) # update

def gen(n):
    prefix = deque([" "] * order) # clear prefix
    result = ''
    random.seed(time.time())
    # prime with some randomness
    for i in range(n):
        prefix.append(random.choice( suffixes['@!@'.join(prefix)] ))
        prefix.popleft()
    while len(result) < n:
        choice = random.choice( suffixes['@!@'.join(prefix)] )
        if choice == " ":
            break
        if len(result) + len(choice) > n - 1:
            break
        result = result + choice + ' '
        prefix.popleft()
        prefix.append(choice)
    return result

if __name__ == "__main__":
    # read and treat input file
    if len(sys.argv) > 1:
        source = sys.argv[1]
    inp = ""
    with open(source, 'rb') as csvfile:
        rows = csv.DictReader(csvfile)
        for row in rows:
            if row['in_reply_to_status_id'] == '':
                inp = inp + row['text'] + ' '
    inp = re.sub('@\S+', '', inp) # remove usernames.
    inp = re.sub('http:\S+', '', inp) # remove links.

    for s in inp.split():
        add(s) # build Markov chain
    add(" ")
    for i in range(1, 10):
        result = '#makyo_ebooks'
        result = gen(140 - len(result)) + result
        print result