Implement traceback.print_stack() and use that to further test generator tracebacks

from_cpython/Lib/traceback.py

@@ -293,13 +293,18 @@ def print_stack(f=None, limit=None, file=None):
     arguments have the same meaning as for print_exception().
     """
 
-    raise NotImplementedError("This function is currently not implemented in Pyston")
-    if f is None:
+    if f is not None or limit is not None:
+        raise NotImplementedError("print_stack() does not currently support the 'f' or 'limit' arguments in Pyston")
+
     try:
         raise ZeroDivisionError
     except ZeroDivisionError:
-            f = sys.exc_info()[2].tb_frame.f_back
-    print_list(extract_stack(f, limit), file)
+        # Make use of Pyston's incorrect behavior, that we generate exception tracebacks all the
+        # way to the top stack frame:
+        l = format_exception(*sys.exc_info())[1:-2]
+
+    for s in l:
+        _print(file, s, '')
 
 def format_stack(f=None, limit=None):
     """Shorthand for 'format_list(extract_stack(f, limit))'."""

test/tests/generator_tracebacks.py

+# allow-warning: converting unicode literal to str
+
 # Generators participate in the notional Python stack just like normal function calls do,
 # even if we implement them using separate C stacks.
 #
@@ -5,7 +7,10 @@
 # get inherited when we go into a generator
 
 # exc_info gets passed into generators (at both begin and send()) and cleared like normal on the way out:
+
 import sys
+import traceback
+
 def f12():
     print
     print "f12"
@@ -19,6 +24,7 @@ def f12():
         try:
             raise KeyError()
         except:
+            traceback.print_stack(file=sys.stdout)
             pass
         print "after KeyError:", sys.exc_info()[0]
         yield 2