Word completion for the new readline.set_completer() function.

When completing a simple identifier, it completes keywords, built-ins
and globals in __main__; when completing NAME.NAME..., it evaluates
(!) the expression up to the last dot and completes its attributes.

It's very cool to do "import string" type "string.", hit the
completion key (twice), and see the list of names defined by the
string module!

Tip: to use the tab key as the completion key, call

    readline.parse_and_bind("tab: complete")

Lib/rlcompleter.py

@@ -0,0 +1,108 @@
+"""Word completion for GNU readline 2.0.
+
+This requires the latest extension to the readline module (the
+set_completer() function).  When completing a simple identifier, it
+completes keywords, built-ins and globals in __main__; when completing
+NAME.NAME..., it evaluates (!) the expression up to the last dot and
+completes its attributes.
+
+It's very cool to do "import string" type "string.", hit the
+completion key (twice), and see the list of names defined by the
+string module!
+
+Tip: to use the tab key as the completion key, call
+
+    readline.parse_and_bind("tab: complete")
+
+Notes:
+
+- Exceptions raised by the completer function are *ignored* (and
+generally cause the completion to fail).  This is a feature -- since
+readline sets the tty device in raw (or cbreak) mode, printing a
+traceback wouldn't work well without some complicated hoopla to save,
+reset and restore the tty state.
+
+- The evaluation of the NAME.NAME... form may cause arbitrary
+application defined code to be executed if an object with a
+__getattr__ hook is found.  Since it is the responsibility of the
+application (or the user) to enable this feature, I consider this an
+acceptable risk.  More complicated expressions (e.g. function calls or
+indexing operations) are *not* evaluated.
+
+- GNU readline is also used by the built-in functions input() and
+raw_input(), and thus these also benefit/suffer from the completer
+features.  Clearly an interactive application can benefit by
+specifying its own completer function and using raw_input() for all
+its input.
+
+- When the original stdin is not a tty device, GNU readline is never
+used, and this module (and the readline module) are silently inactive.
+
+"""
+
+import readline
+import keyword
+import __builtin__
+import __main__
+import string
+import re
+import traceback
+
+class Completer:
+
+    def complete(self, text, state):
+	"""Return the next possible completion for 'text'.
+
+	This is called successively with state == 0, 1, 2, ... until it
+	returns None.  The completion should begin with 'text'.
+
+	"""
+	if state == 0:
+	    if "." in text:
+		self.matches = self.attr_matches(text)
+	    else:
+		self.matches = self.global_matches(text)
+	return self.matches[state]
+
+    def global_matches(self, text):
+	"""Compute matches when text is a simple name.
+
+	Return a list of all keywords, built-in functions and names
+	currently defines in __main__ that match.
+
+	"""
+	matches = []
+	n = len(text)
+	for list in [keyword.kwlist,
+		     __builtin__.__dict__.keys(),
+		     __main__.__dict__.keys()]:
+	    for word in list:
+		if word[:n] == text:
+		    matches.append(word)
+	return matches
+
+    def attr_matches(self, text):
+	"""Compute matches when text contains a dot.
+
+	Assuming the text is of the form NAME.NAME....[NAME], and is
+	evaluabable in the globals of __main__, it will be evaluated
+	and its attributes (as revealed by dir()) are used as possible
+	completions.
+
+	WARNING: this can still invoke arbitrary C code, if an object
+	with a __getattr__ hook is evaluated.
+
+	"""
+	m = re.match(r"(\w+(\.\w+)*)\.(\w*)", text)
+	if not m:
+	    return
+	expr, attr = m.group(1, 3)
+	words = dir(eval(expr, __main__.__dict__))
+	matches = []
+	n = len(attr)
+	for word in words:
+	    if word[:n] == attr:
+		matches.append("%s.%s" % (expr, word))
+	return matches
+
+readline.set_completer(Completer().complete)