Trac #18799: Python 3 preparation: Change syntax of raise with traceback

{{{2to3}}} proposes changes for
{{{
raise E, V, T -> raise E(V).with_traceback(T)
raise E, None, T -> raise E.with_traceback(T)
}}}
These changes are invalid (see also #18796).

Several options are given in the documentation of python-future (see
http://python-future.org/compatible_idioms.html#raising-exceptions).

This ticket is tracked as a dependency of meta-ticket #16052.
The simple {{{raise}}} statements are fixed in #15990.

URL: http://trac.sagemath.org/18799
Reported by: wluebbe
Ticket author(s): Wilfried Luebbe
Reviewer(s): Frédéric Chapoton

src/sage/interfaces/expect.py

@@ -67,6 +67,8 @@
 from sage.env import SAGE_EXTCODE, LOCAL_IDENTIFIER
 from sage.misc.object_multiplexer import Multiplex
 
+from six import reraise as raise_
+
 BAD_SESSION = -2
 
 # The subprocess is a shared resource.  In a multi-threaded
@@ -883,7 +885,7 @@ def _eval_line(self, line, allow_use_file=True, wait_for_prompt=True, restart_if
                         except (TypeError, RuntimeError):
                             pass
                         return self._eval_line(line,allow_use_file=allow_use_file, wait_for_prompt=wait_for_prompt, restart_if_needed=False)
-                raise RuntimeError, "%s\nError evaluating %s in %s"%(msg, line, self), sys.exc_info()[2]
+                raise_(RuntimeError, "%s\nError evaluating %s in %s"%(msg, line, self), sys.exc_info()[2])
 
             if len(line)>0:
                 try:
@@ -1329,7 +1331,7 @@ def __init__(self, parent, value, is_name=False, name=None):
             # coercion to work properly.
             except (RuntimeError, ValueError) as x:
                 self._session_number = -1
-                raise TypeError, x, sys.exc_info()[2]
+                raise_(TypeError, x, sys.exc_info()[2])
             except BaseException:
                 self._session_number = -1
                 raise

src/sage/interfaces/singular.py

@@ -334,6 +334,8 @@
 from sage.misc.misc import get_verbose
 from sage.misc.superseded import deprecation
 
+from six import reraise as raise_
+
 class SingularError(RuntimeError):
     """
     Raised if Singular printed an error message
@@ -1261,7 +1263,7 @@ def __init__(self, parent, type, value, is_name=False):
             # coercion to work properly.
             except SingularError as x:
                 self._session_number = -1
-                raise TypeError, x, sys.exc_info()[2]
+                raise_(TypeError, x, sys.exc_info()[2])
             except BaseException:
                 self._session_number = -1
                 raise

src/sage/schemes/elliptic_curves/ell_number_field.py

@@ -109,6 +109,8 @@
 
 import gal_reps_number_field
 
+from six import reraise as raise_
+
 class EllipticCurve_number_field(EllipticCurve_field):
     r"""
     Elliptic curve over a number field.
@@ -893,7 +895,7 @@ def _reduce_model(self):
             (a1, a2, a3, a4, a6) = [ZK(a) for a in self.a_invariants()]
         except TypeError:
             import sys
-            raise TypeError, "_reduce_model() requires an integral model.", sys.exc_info()[2]
+            raise_(TypeError, "_reduce_model() requires an integral model.", sys.exc_info()[2])
 
         # N.B. Must define s, r, t in the right order.
         if ZK.absolute_degree() == 1: