random password generator

randpass.py

import os 
import string

letters = string.letters 
lowercase = string.lowercase
uppercase = string.uppercase
digits = string.digits 
punctuation = string.punctuation 
all_nospace = digits + letters + punctuation 

def generate_map(collection): 
    collection = "".join(list(set(list(collection))))
    klen = len(collection) 
    h = 255 / klen
    i = 0
    k = 0
    table = {} 
    while i < 256: 
        if k >= klen: 
            break
        for j in range(h): 
            table[i+j] = collection[k] 
        i += h 
        k += 1 
    if 255 % len(collection):
        t = len(table)
        for i in range(256 - t): 
            table[t+i] = collection[i]
    return table

def generate(length, collection, mapcache=False): 
    if length < 1 or length > 255:
        return None
    result = []
    if mapcache:
        table = mapcache
    else:
        table = generate_map(collection)
    while len(result) != length:
        for i in os.urandom(length): 
            result.append(table[ord(i)]) 
    return "".join(result)
        
if __name__ == "__main__": 
    print generate(16, letters+digits)