rand-string.arc

(def rand-string (n)
  (let c "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    (with (nc 62 s (newstring n) i 0)
      (w/infile str "/dev/urandom"
        (while (< i n)
          (let x (readb str)
             (unless (> x 247)
               (= (s i) (c (mod x nc)))
               (++ i)))))
      s)))

rand-string.py

def rand_string(n):
    c = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    newstring = ""
    read_position = 1
    with open('/dev/urandom', 'r') as f:
        while(len(newstring) < 4):
            f.seek(read_position)
            ordinal = ord(f.read(1))
            if not ordinal > 247:
                newstring += c[ordinal % 62]
            read_position += 1
    return newstring

print (rand_string(4))