Simplify debugger classes.

Directly get the color scheme from the interactive shell (which is
created if not already present, anyways).  The goal is ultimately to
allow the IPython debugger to be a drop-in replacement of the stdlib pdb
with the same signature (in particular, this would obviate the need for
plugins such as nose-ipdb and pytest-ipdb; nose and pytest could instead
let their `--pdb` command line arg take an argument specifying the Pdb
(sub)class to use, e.g. `py.test --pdb=IPython.core.debugger.Pdb`).

Also deprecate the `Tracer` class (and related utilities), which can be
fairly trivially replaced by `IPython.core.debugger.Pdb().set_trace()`
(we can let `Pdb` catch `BdbQuit` itself).

IPython/core/debugger.py

@@ -30,6 +30,7 b' import bdb'
 import functools
 import inspect
 import sys
+import warnings
 
 from IPython import get_ipython
 from IPython.utils import PyColorize, ulinecache
@@ -62,6 +63,8 b' def BdbQuit_excepthook(et, ev, tb, excepthook=None):'
     All other exceptions are processed using the `excepthook`
     parameter.
     """
+    warnings.warn("`BdbQuit_excepthook` is deprecated since version 5.1",
+                  DeprecationWarning)
     if et==bdb.BdbQuit:
         print('Exiting Debugger.')
     elif excepthook is not None:
@@ -70,7 +73,11 b' def BdbQuit_excepthook(et, ev, tb, excepthook=None):'
         # Backwards compatibility. Raise deprecation warning?
         BdbQuit_excepthook.excepthook_ori(et,ev,tb)
 
+
 def BdbQuit_IPython_excepthook(self,et,ev,tb,tb_offset=None):
+    warnings.warn(
+        "`BdbQuit_IPython_excepthook` is deprecated since version 5.1",
+        DeprecationWarning)
     print('Exiting Debugger.')
 
 
@@ -114,6 +121,9 b' class Tracer(object):'
         step through code, set breakpoints, etc.  See the pdb documentation
         from the Python standard library for usage details.
         """
+        warnings.warn("`Tracer` is deprecated since version 5.1, directly use "
+                      "`IPython.core.debugger.Pdb.set_trace()`",
+                      DeprecationWarning)
 
         ip = get_ipython()
         if ip is None:
@@ -189,12 +199,12 b' def _file_lines(fname):'
 class Pdb(OldPdb, object):
     """Modified Pdb class, does not load readline."""
 
-    def __init__(self,color_scheme='NoColor',completekey=None,
+    def __init__(self, color_scheme=None, completekey=None,
                  stdin=None, stdout=None, context=5):
 
         # Parent constructor:
         try:
-            self.context=int(context)
+            self.context = int(context)
             if self.context <= 0:
                 raise ValueError("Context must be a positive integer")
         except (TypeError, ValueError):
@@ -211,6 +221,13 b' class Pdb(OldPdb, object):'
                 TerminalInteractiveShell
             self.shell = TerminalInteractiveShell.instance()
 
+        if color_scheme is not None:
+            warnings.warn(
+                "The `color_scheme` argument is deprecated since version 5.1",
+                DeprecationWarning)
+        else:
+            color_scheme = self.shell.colors
+
         self.aliases = {}
 
         # Create color table: we copy the default one from the traceback
@@ -250,6 +267,12 b' class Pdb(OldPdb, object):'
         """Shorthand access to the color table scheme selector method."""
         self.color_scheme_table.set_active_scheme(scheme)
 
+    def trace_dispatch(self, frame, event, arg):
+        try:
+            return super(Pdb, self).trace_dispatch(frame, event, arg)
+        except bdb.BdbQuit:
+            pass
+
     def interaction(self, frame, traceback):
         try:
             OldPdb.interaction(self, frame, traceback)

IPython/core/magics/execution.py

@@ -801,7 +801,7 b' python-profiler package from non-free.""")'
             If the break point given by `bp_line` is not valid.
 
         """
-        deb = debugger.Pdb(self.shell.colors)
+        deb = debugger.Pdb()
         # reset Breakpoint state, which is moronically kept
         # in a class
         bdb.Breakpoint.next = 1