Hooks now implement "Chain of Command" design pattern,

with TryNext exception signalling failure. Setting
via set_hook as usual.

IPython/hooks.py

@@ -32,7 +32,7 b" ip_set_hook('editor',myiphooks.calljed)"
 The ip_set_hook function is put by IPython into the builtin namespace, so it
 is always available from all running code.
 
-$Id: hooks.py 988 2006-01-02 21:21:47Z fperez $"""
+$Id: hooks.py 1019 2006-01-14 13:02:12Z vivainio $"""
 
 #*****************************************************************************
 #       Copyright (C) 2005 Fernando Perez. <[e-mail]>
@@ -46,7 +46,7 b" __author__ = '%s <%s>' % Release.authors['Fernando']"
 __license__ = Release.license
 __version__ = Release.version
 
-import os
+import os,bisect
 
 # List here all the default hooks.  For now it's just the editor functions
 # but over time we'll move here all the public API for user-accessible things.
@@ -93,3 +93,44 b' def fix_error_editor(self,filename,linenum,column,msg):'
         os.system('vim --cmd "set errorformat=%f:%l:%c:%m" -q ' + t.name)
     finally:
         t.close()
+
+class TryNext(Exception):
+    pass
+
+class CommandChainDispatcher:
+    """ Dispatch calls to a chain of commands until some func can handle it
+    
+    Usage: instantiate, execute "add" to add commands (with optional
+    priority), execute normally via f() calling mechanism.
+    
+    """
+    def __init__(self,commands=None):
+        if commands is None:
+            self.chain = []
+        else:
+            self.chain = commands
+            
+            
+    def __call__(self,*args, **kw):
+        """ Command chain is called just like normal func. 
+        
+        This will call all funcs in chain with the same args as were given to this
+        function, and return the result of first func that didn't raise
+        TryNext """
+        
+        for prio,cmd in self.chain:
+            #print "prio",prio,"cmd",cmd #dbg
+            try:
+                ret = cmd(*args, **kw)
+                return ret
+            except TryNext:
+                pass
+                
+    def __str__(self):
+        return str(self.chain)
+    
+    def add(self, func, priority=0):
+        """ Add a func to the cmd chain with given priority """
+        bisect.insort(self.chain,(priority,func))
+
+        
  No newline at end of file

IPython/ipapi.py

@@ -90,8 +90,9 b' def expose_magic(magicname, func):'
     '''
     
     from IPython import Magic
-    
-    setattr(Magic.Magic, "magic_" + magicname, func)
+    import new
+    im = new.instancemethod(func,__IP, __IP.__class__)
+    setattr(__IP, "magic_" + magicname, im)
 
 class asmagic:
     """ Decorator for exposing magics in a friendly 2.4 decorator form 
@@ -121,11 +122,12 b' class ashook:'
     
     """
     
-    def __init__(self,name):
+    def __init__(self,name,priority=50):
         self.name = name
+        self.prio = priority
         
     def __call__(self,f):
-        set_hook(self.name, f)
+        set_hook(self.name, f, self.prio)
         return f
 
 

IPython/iplib.py

@@ -6,7 +6,7 b' Requires Python 2.3 or newer.'
 
 This file contains all the classes and helper functions specific to IPython.
 
-$Id: iplib.py 1017 2006-01-14 09:46:45Z vivainio $
+$Id: iplib.py 1019 2006-01-14 13:02:12Z vivainio $
 """
 
 #*****************************************************************************
@@ -401,7 +401,8 b' class InteractiveShell(object,Magic):'
         # Set all default hooks, defined in the IPython.hooks module.
         hooks = IPython.hooks
         for hook_name in hooks.__all__:
-            self.set_hook(hook_name,getattr(hooks,hook_name))
+            # default hooks have priority 100, i.e. low; user hooks should have 0-100 priority
+            self.set_hook(hook_name,getattr(hooks,hook_name), 100)
 
         # Flag to mark unconditional exit
         self.exit_now = False
@@ -707,17 +708,31 b' class InteractiveShell(object,Magic):'
                 __builtin__.__dict__[biname] = bival
         self.builtins_added.clear()
     
-    def set_hook(self,name,hook):
+    def set_hook(self,name,hook, priority = 50):
         """set_hook(name,hook) -> sets an internal IPython hook.
 
         IPython exposes some of its internal API as user-modifiable hooks.  By
-        resetting one of these hooks, you can modify IPython's behavior to
-        call at runtime your own routines."""
+        adding your function to one of these hooks, you can modify IPython's 
+        behavior to call at runtime your own routines."""
 
         # At some point in the future, this should validate the hook before it
         # accepts it.  Probably at least check that the hook takes the number
         # of args it's supposed to.
-        setattr(self.hooks,name,new.instancemethod(hook,self,self.__class__))
+        dp = getattr(self.hooks, name, None)
+        if not dp:
+            dp = IPython.hooks.CommandChainDispatcher()
+        
+        f = new.instancemethod(hook,self,self.__class__)
+        try:
+            dp.add(f,priority)
+        except AttributeError:
+            # it was not commandchain, plain old func - replace
+            dp = f
+
+        setattr(self.hooks,name, dp)
+        
+        
+        #setattr(self.hooks,name,new.instancemethod(hook,self,self.__class__))
 
     def set_custom_exc(self,exc_tuple,handler):
         """set_custom_exc(exc_tuple,handler)

doc/ChangeLog

@@ -9,6 +9,12 b''
 	backslash (as yielded by tab completer) is still space;
 	"%cd long\ name" works as expected.
 
+	* IPython/ipapi.py,hooks.py,iplib.py: Hooks now implemented
+	as "chain of command", with priority. API stays the same, 
+	TryNext exception raised by a hook function signals that 
+	current hook failed and next hook should try handling it, as 
+	suggested by Walter Dörwald <[e-mail]>.
+
 
 2006-01-13  Ville Vainio  <[e-mail]>