You can use the glob module:
>>> import glob
>>> print len(glob.glob('/tmp/*'))
10
Or, as Mark Byers suggests in his answer, if you only want files:
>>> print [f for f in glob.glob('/tmp/*') if os.path.isfile(f)]
['/tmp/foo']
>>> print sum(os.path.isfile(f) for f in glob.glob('/tmp/*'))
1