Python 2.6 generator rule with 'and' conditional

Fixes #283.

test/simple_source/bug26/00_generator.py

@@ -0,0 +1,7 @@
+# Issue #283 in Python 2.6
+# See https://github.com/rocky/python-uncompyle6/issues/283
+
+# This code is RUNNABLE!
+
+G = ( c for c in "spam, Spam, SPAM!" if c > 'A' and c < 'S')
+assert list(G) == ["P", "M"]

uncompyle6/parsers/parse26.py

@@ -241,6 +241,9 @@ class Python26Parser(Python2Parser):
         genexpr_func ::= setup_loop_lf FOR_ITER store comp_iter JUMP_ABSOLUTE come_froms
                          POP_TOP jb_pop jb_pb_come_from
 
+        genexpr_func ::= setup_loop_lf FOR_ITER store comp_iter JUMP_BACK come_froms
+                         POP_TOP jb_pb_come_from
+
         generator_exp ::= LOAD_GENEXPR MAKE_FUNCTION_0 expr GET_ITER CALL_FUNCTION_1 COME_FROM
         list_if ::= list_if ::= expr jmp_false_then list_iter
         '''

uncompyle6/parsers/parse27.py

@@ -234,7 +234,7 @@ class Python27Parser(Python2Parser):
             return invalid
 
         if rule == ('and', ('expr', 'jmp_false', 'expr', '\\e_come_from_opt')):
-            # If the instruction after the instructions formin "and"  is an "YIELD_VALUE"
+            # If the instruction after the instructions forming "and" is a "YIELD_VALUE"
             # then this is probably an "if" inside a comprehension.
             if tokens[last] == 'YIELD_VALUE':
                 # Note: We might also consider testing last+1 being "POP_TOP"
@@ -243,6 +243,9 @@ class Python27Parser(Python2Parser):
             # Test that jmp_false jumps to the end of "and"
             # or that it jumps to the same place as the end of "and"
             jmp_false = ast[1][0]
+
+            # FIXME: if the jmp_false is POP_JUMP_IF_FALSE is the address
+            # is *absoulte* and the calulation below is wrong!
             jmp_target = jmp_false.offset + jmp_false.attr + 3
             return not (jmp_target == tokens[last].offset or
                         tokens[last].pattr == jmp_false.pattr)