Reset readline delimiters after loading rmagic.

Closes gh-2759

IPython/core/interactiveshell.py

@@ -358,6 +358,7 b' class InteractiveShell(SingletonConfigurable):'
     # but for now, we can't do that as readline is welded in everywhere.
     readline_use = CBool(True, config=True)
     readline_remove_delims = Unicode('-/~', config=True)
+    readline_delims = Unicode() # set by init_readline()
     # don't use \M- bindings by default, because they
     # conflict with 8-bit encodings. See gh-58,gh-88
     readline_parse_and_bind = List([
@@ -1866,6 +1867,9 b' class InteractiveShell(SingletonConfigurable):'
                 delims = delims.replace(d, "")
             delims = delims.replace(ESC_MAGIC, '')
             readline.set_completer_delims(delims)
+            # Store these so we can restore them if something like rpy2 modifies
+            # them.
+            self.readline_delims = delims
             # otherwise we end up with a monster history after a while:
             readline.set_history_length(self.history_length)
 

IPython/extensions/rmagic.py

@@ -617,3 +617,7 b' __doc__ = __doc__.format('
 def load_ipython_extension(ip):
     """Load the extension in IPython."""
     ip.register_magics(RMagics)
+    # Initialising rpy2 interferes with readline. Since, at this point, we've
+    # probably just loaded rpy2, we reset the delimiters. See issue gh-2759.
+    if ip.has_readline:
+        ip.readline.set_completer_delims(ip.readline_delims)