Catch errors in querying readline which occur with pyreadline.

IPython/core/interactiveshell.py

@@ -144,14 +144,18 b' class ReadlineNoRecord(object):'
         
     def __enter__(self):
         if self._nested_level == 0:
+            try:
             self.orig_length = self.current_length()
             self.readline_tail = self.get_readline_tail()
+            except (AttributeError, IndexError):   # Can fail with pyreadline
+                self.orig_length, self.readline_tail = 999999, []
         self._nested_level += 1
         
     def __exit__(self, type, value, traceback):
         self._nested_level -= 1
         if self._nested_level == 0:
             # Try clipping the end if it's got longer
+            try:
             e = self.current_length() - self.orig_length
             if e > 0:
                 for _ in range(e):
@@ -161,6 +165,8 b' class ReadlineNoRecord(object):'
             if self.current_length() != self.orig_length \
                 or self.get_readline_tail() != self.readline_tail:
                 self.shell.refill_readline_hist()
+            except (AttributeError, IndexError):
+                pass
         # Returning False will cause exceptions to propagate
         return False