diff --git a/mercurial/hook.py b/mercurial/hook.py
new file mode 100644
--- /dev/null
+++ b/mercurial/hook.py
@@ -0,0 +1,96 @@
+# hook.py - hook support for mercurial
+#
+# Copyright 2007 Matt Mackall <mpm@selenic.com>
+#
+# This software may be used and distributed according to the terms
+# of the GNU General Public License, incorporated herein by reference.
+
+from i18n import _
+import util
+
+def _pythonhook(ui, repo, name, hname, funcname, args, throw):
+    '''call python hook. hook is callable object, looked up as
+    name in python module. if callable returns "true", hook
+    fails, else passes. if hook raises exception, treated as
+    hook failure. exception propagates if throw is "true".
+
+    reason for "true" meaning "hook failed" is so that
+    unmodified commands (e.g. mercurial.commands.update) can
+    be run as hooks without wrappers to convert return values.'''
+
+    ui.note(_("calling hook %s: %s\n") % (hname, funcname))
+    obj = funcname
+    if not callable(obj):
+        d = funcname.rfind('.')
+        if d == -1:
+            raise util.Abort(_('%s hook is invalid ("%s" not in '
+                               'a module)') % (hname, funcname))
+        modname = funcname[:d]
+        try:
+            obj = __import__(modname)
+        except ImportError:
+            try:
+                # extensions are loaded with hgext_ prefix
+                obj = __import__("hgext_%s" % modname)
+            except ImportError:
+                raise util.Abort(_('%s hook is invalid '
+                                   '(import of "%s" failed)') %
+                                 (hname, modname))
+        try:
+            for p in funcname.split('.')[1:]:
+                obj = getattr(obj, p)
+        except AttributeError, err:
+            raise util.Abort(_('%s hook is invalid '
+                               '("%s" is not defined)') %
+                             (hname, funcname))
+        if not callable(obj):
+            raise util.Abort(_('%s hook is invalid '
+                               '("%s" is not callable)') %
+                             (hname, funcname))
+    try:
+        r = obj(ui=ui, repo=repo, hooktype=name, **args)
+    except (KeyboardInterrupt, util.SignalInterrupt):
+        raise
+    except Exception, exc:
+        if isinstance(exc, util.Abort):
+            ui.warn(_('error: %s hook failed: %s\n') %
+                         (hname, exc.args[0]))
+        else:
+            ui.warn(_('error: %s hook raised an exception: '
+                           '%s\n') % (hname, exc))
+        if throw:
+            raise
+        ui.print_exc()
+        return True
+    if r:
+        if throw:
+            raise util.Abort(_('%s hook failed') % hname)
+        ui.warn(_('warning: %s hook failed\n') % hname)
+    return r
+
+def _exthook(ui, repo, name, cmd, args, throw):
+    ui.note(_("running hook %s: %s\n") % (name, cmd))
+    env = dict([('HG_' + k.upper(), v) for k, v in args.iteritems()])
+    r = util.system(cmd, environ=env, cwd=repo.root)
+    if r:
+        desc, r = util.explain_exit(r)
+        if throw:
+            raise util.Abort(_('%s hook %s') % (name, desc))
+        ui.warn(_('warning: %s hook %s\n') % (name, desc))
+    return r
+
+def hook(ui, repo, name, throw=False, **args):
+    r = False
+    hooks = [(hname, cmd) for hname, cmd in ui.configitems("hooks")
+             if hname.split(".", 1)[0] == name and cmd]
+    hooks.sort()
+    for hname, cmd in hooks:
+        if callable(cmd):
+            r = _pythonhook(ui, repo, name, hname, cmd, args, throw) or r
+        elif cmd.startswith('python:'):
+            r = _pythonhook(ui, repo, name, hname, cmd[7:].strip(),
+                            args, throw) or r
+        else:
+            r = _exthook(ui, repo, hname, cmd, args, throw) or r
+    return r
+