move sentinel out of IPython.utils.signature

signature is a backport of a stdlib file,
and not an appropriate place for new code.

Further, to avoid adding a new trivial module to genutils,
a copy is added each place we've used a sentinel

IPython/utils/sentinel.py

@@ -0,0 +1,17 b''
+"""Sentinel class for constants with useful reprs"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+class Sentinel(object):
+
+    def __init__(self, name, module, docstring=None):
+        self.name = name
+        self.module = module
+        if docstring:
+            self.__doc__ = docstring
+
+
+    def __repr__(self):
+        return str(self.module)+'.'+self.name
+

jupyter_nbformat/sentinel.py

@@ -0,0 +1,17 b''
+"""Sentinel class for constants with useful reprs"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+class Sentinel(object):
+
+    def __init__(self, name, module, docstring=None):
+        self.name = name
+        self.module = module
+        if docstring:
+            self.__doc__ = docstring
+
+
+    def __repr__(self):
+        return str(self.module)+'.'+self.name
+

traitlets/sentinel.py

@@ -0,0 +1,17 b''
+"""Sentinel class for constants with useful reprs"""
+
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+class Sentinel(object):
+
+    def __init__(self, name, module, docstring=None):
+        self.name = name
+        self.module = module
+        if docstring:
+            self.__doc__ = docstring
+
+
+    def __repr__(self):
+        return str(self.module)+'.'+self.name
+

IPython/core/formatters.py

@@ -21,7 +21,7 b' from decorator import decorator'
 
 from IPython.config.configurable import Configurable
 from IPython.core.getipython import get_ipython
-from IPython.utils.signatures import Sentinel
+from IPython.utils.sentinel import Sentinel
 from IPython.lib import pretty
 from IPython.utils.traitlets import (
     Bool, Dict, Integer, Unicode, CUnicode, ObjectName, List,

IPython/utils/signatures.py

@@ -815,18 +815,3 b' class Signature(object):'
 
         return rendered
 
-## Fake unique value as KWargs, in some places.
-# do not put docstrings here or they will appear 
-# on created fake values.
-class Sentinel(object):
-
-    def __init__(self, name, module, docstring=None):
-        self.name = name
-        self.module = module
-        if docstring:
-            self.__doc__ = docstring
-
-
-    def __repr__(self):
-        return str(self.module)+'.'+self.name
-

jupyter_nbformat/__init__.py

@@ -14,7 +14,7 b' from . import v1'
 from . import v2
 from . import v3
 from . import v4
-from IPython.utils.signatures import Sentinel
+from .sentinel import Sentinel
 
 __all__ = ['versions', 'validate', 'ValidationError', 'convert', 'from_dict',
            'NotebookNode', 'current_nbformat', 'current_nbformat_minor',

traitlets/traitlets.py

@@ -56,11 +56,11 b' from warnings import warn'
 from IPython.utils import py3compat
 from IPython.utils import eventful
 from IPython.utils.getargspec import getargspec
-from IPython.utils.signatures import Sentinel
 from IPython.utils.importstring import import_item
 from IPython.utils.py3compat import iteritems, string_types
 from IPython.testing.skipdoctest import skip_doctest
 
+from .sentinel import Sentinel
 SequenceTypes = (list, tuple, set, frozenset)
 
 #-----------------------------------------------------------------------------