Nathan Ostgard

In Python:

import os.path, random, string
def random_filename(chars=string.hexchars, length=16, prefix='', suffix='', \
                    verify=True, attempts=10):
  for attempt in range(attempts):
    filename = ''.join([random.choice(chars) for i in range(length)])
    filename = prefix + filename + suffix
    if not verify or not os.path.exists(filename):
      return filename

>>> random_filename()
'DC53e02B08eF47e9'
>>> random_filename(chars='hi', length=32)
'hhhihihhhiiihhhihhiiiiiihhhhiihh'
>>> random_filename(prefix='username', suffix='.txt')
'username7dbd29aBdD25BeB9.txt'

# returns None if it can't find a filename
>>> open('xxx', 'w').close()
>>> str(random_filename(chars='x', length=3))
'None'

In Ruby:

def random_filename(opts={})
  opts = {:chars => ('0'..'9').to_a + ('A'..'F').to_a + ('a'..'f').to_a,
          :length => 16, :prefix => '', :suffix => '',
          :verify => true, :attempts => 10}.merge(opts)
  opts[:attempts].times do
    filename = ''
    opts[:length].times { filename << opts[:chars][rand(opts[:chars].size)] }
    filename = opts[:prefix] + filename + opts[:suffix]
    return filename unless opts[:verify] && File.exists?(filename)
  end
  nil
end