Half-working filename tab-completer. Play with it--it mostly works, but you have to help it along more than you're used to at the command line.

simple_file_completer.py

#!/usr/bin/env python
import readline
import os
import re
from pprint import *

# This will tab-complete from the working directory, starting from /, and going through the sub-directories,
# but it doesn't behave quite the way you expect.  
# For instance, it chooses for you if there are two partial matches.
# The readline call to def complete does not pass a 
# leading "/" in the "text" variable, so I had to start using get_line_buffer and really don't find 
# much use for the variables "text" and "state".
# Isn't there a "right" way to do this?  It seems like it ought to be a built-in in readline!
# Not sure what RE_SPACE is for.

RE_SPACE = re.compile('.*\s+$', re.M)

COMMANDS = os.listdir('.')

def complete(text, state):
    line = readline.get_line_buffer().split()
    # NOTE THAT THE LEADING / WILL NOT COME THROUGH IN text.
    try:
        if line == []:
            path = "."
            COMMANDS = os.listdir(path)
        elif line[0] == "/":   # Readline will never return a leading "/".
            COMMANDS = os.listdir("/")
        elif line == "" or line == "." or line == "./":
            path = "."
            COMMANDS = os.listdir(path)
        else:
            if "/" in line[0]:
                if line[0] == "/":
                    base_path = "/"
                else:
                    base_path = line[0].rsplit("/",1)[0] + "/"
                    partial_file_name = line[0].rsplit("/")[-1]
            else:
                base_path = "."
                partial_file_name = line[0]
            COMMANDS = os.listdir(base_path)
            for one_file in COMMANDS:   
                if one_file.startswith(partial_file_name):
                    if not state:
                        return one_file

    except:
        print "exception"
        COMMANDS = os.listdir(".")

    for one_file in COMMANDS:
        if one_file.startswith(text) and state == 0:
            return one_file
        else:
            state -= 1


readline.parse_and_bind("tab: complete")
readline.set_completer(complete)
while True:
    file_name = raw_input('Enter filename: ')
    print file_name
    

There's a new working version in good shape on gist https://gist.github.com/4040404/ with credits in the comments.