example

$ python secret123.py
f3M8VZEHb2/VAuKJScJAMYNuiawQr8q2^%s+K@ShK2M

secret123.py

#!/usr/bin/env python
from base64 import b64encode
from hashlib import sha256 as sha

INPUT_BYTE_COUNT = 4096
REPLACE = {
    'O': '@',
    '0': '$',
    'o': '%',
    '1': '^',
    'l': '&',
    'I': '*',
}

def replace_chars(s):
    for i, j in REPLACE.items():
        s = s.replace(i, j)
    return s

def pwgen():
    random_bytes = open('/dev/random').read(INPUT_BYTE_COUNT)
    assert len(random_bytes) == INPUT_BYTE_COUNT
    digest = sha(random_bytes).digest()
    return replace_chars(b64encode(digest).rstrip('='))

if __name__ == '__main__':
    print pwgen()