Generate a bcrypt password with salt only using `/dev/random` and with unambiguous characters

generate_password.py

#!/usr/bin/env python2
from __future__ import print_function, division

from itertools import (
    ifilter,
    islice,
    imap,
)
from functools import partial
import operator
import string
import sys

try:
    import bcrypt
except ImportError as ie:
    raise ImportError(
        "bcrypt missing, install bcrypt by running:\n"
        "sudo pip install bcrypt"
    )


def take(sequence, n):
    return list(islice(sequence, n))

valid_characters = "".join(set(string.letters + string.digits) - set("lI10OQ"))

multiplier = (ord('\xff') + 1) // len(valid_characters)
assert(multiplier > 0)

n_characters = 12

in_valid_character_range = lambda c: ord(c) < multiplier * len(valid_characters)
to_valid_character = lambda c: valid_characters[ord(c) // multiplier]

random_bytes = iter(lambda: open("/dev/random", "rb").read(1), None)
random_characters = imap(
    to_valid_character,
    ifilter(
        in_valid_character_range,
        random_bytes
    )
)

def new_password(n_characters):
    password = "".join(
        take(
            random_characters,
            n_characters
        )
    ).encode('utf-8')

    return password

print("Wave your mouse to generate entropy, it can take a few seconds to get enough")
password = new_password(n_characters)
print("Password: {}".format(password))

password_hash = bcrypt.hashpw(password, bcrypt.gensalt())
print("Hash: {}".format(password_hash))

print("Verify password and hash .. ", end='')
if bcrypt.checkpw(password, password_hash):
    print("OK") 
else:
    print("Fail")
    sys.exit(1)