Merge pull request #1703 from takluyver/i211

Allow TryNext to have an error message without it affecting the command chain

added as `_msg`, relaying `**kwargs`

closes  #211

IPython/core/error.py

@@ -1,59 +1,66 b''
 # encoding: utf-8
 """
 Global exception classes for IPython.core.
 
 Authors:
 
 * Brian Granger
 * Fernando Perez
 * Min Ragan-Kelley
 
 Notes
 -----
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Exception classes
 #-----------------------------------------------------------------------------
 
 class IPythonCoreError(Exception):
     pass
 
 
 class TryNext(IPythonCoreError):
     """Try next hook exception.
 
     Raise this in your hook function to indicate that the next hook handler
     should be used to handle the operation.  If you pass arguments to the
     constructor those arguments will be used by the next hook instead of the
     original ones.
+    
+    A _msg argument will not be passed on, so it can be used as a displayable
+    error message.
     """
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, _msg="", *args, **kwargs):
         self.args = args
         self.kwargs = kwargs
+        self.msg = _msg
+    
+    def __str__(self):
+        return str(self.msg)
 
 class UsageError(IPythonCoreError):
     """Error in magic function arguments, etc.
 
     Something that probably won't warrant a full traceback, but should
     nevertheless interrupt a macro / batch file.
     """
 
 class StdinNotImplementedError(IPythonCoreError, NotImplementedError):
     """raw_input was requested in a context where it is not supported
 
     For use in IPython kernels, where only some frontends may support
     stdin requests.
     """

IPython/lib/clipboard.py

@@ -1,56 +1,56 b''
 """ Utilities for accessing the platform's clipboard.
 """
 
 import subprocess
 import sys
 
 from IPython.core.error import TryNext
 
 
 def win32_clipboard_get():
     """ Get the current clipboard's text on Windows.
 
     Requires Mark Hammond's pywin32 extensions.
     """
     try:
         import win32clipboard
     except ImportError:
         message = ("Getting text from the clipboard requires the pywin32 "
             "extensions: http://sourceforge.net/projects/pywin32/")
-        raise TryNext(message)
+        raise TryNext(_msg=message)
     win32clipboard.OpenClipboard()
     text = win32clipboard.GetClipboardData(win32clipboard.CF_TEXT)
     # FIXME: convert \r\n to \n?
     win32clipboard.CloseClipboard()
     return text
 
 def osx_clipboard_get():
     """ Get the clipboard's text on OS X.
     """
     p = subprocess.Popen(['pbpaste', '-Prefer', 'ascii'],
         stdout=subprocess.PIPE)
     text, stderr = p.communicate()
     # Text comes in with old Mac \r line endings. Change them to \n.
     text = text.replace('\r', '\n')
     return text
 
 def tkinter_clipboard_get():
     """ Get the clipboard's text using Tkinter.
 
     This is the default on systems that are not Windows or OS X. It may
     interfere with other UI toolkits and should be replaced with an
     implementation that uses that toolkit.
     """
     try:
         import Tkinter
     except ImportError:
         message = ("Getting text from the clipboard on this platform "
             "requires Tkinter.")
-        raise TryNext(message)
+        raise TryNext(_msg=message)
     root = Tkinter.Tk()
     root.withdraw()
     text = root.clipboard_get()
     root.destroy()
     return text