perf scripts python: Add Python 3 support to Core.py

Support both Python 2 and Python 3 in Core.py. This should have no
functional change.
Signed-off-by: Jeremy Cline <jeremy@jcline.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Herton Krzesinski <herton@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/0100016341a72ebe-e572899e-f445-4765-98f0-c314935727f9-000000@email.amazonses.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/python/Perf-Trace-Util/lib/Perf/Trace/Core.py

@@ -32,9 +32,7 @@ def flag_str(event_name, field_name, value):
 
     if flag_fields[event_name][field_name]:
         print_delim = 0
-        keys = flag_fields[event_name][field_name]['values'].keys()
-        keys.sort()
-        for idx in keys:
+        for idx in sorted(flag_fields[event_name][field_name]['values']):
             if not value and not idx:
                 string += flag_fields[event_name][field_name]['values'][idx]
                 break
@@ -51,9 +49,7 @@ def symbol_str(event_name, field_name, value):
     string = ""
 
     if symbolic_fields[event_name][field_name]:
-        keys = symbolic_fields[event_name][field_name]['values'].keys()
-        keys.sort()
-        for idx in keys:
+        for idx in sorted(symbolic_fields[event_name][field_name]['values']):
             if not value and not idx:
                 string = symbolic_fields[event_name][field_name]['values'][idx]
                 break
@@ -74,9 +70,7 @@ def trace_flag_str(value):
     string = ""
     print_delim = 0
 
-    keys = trace_flags.keys()
-
-    for idx in keys:
+    for idx in trace_flags:
         if not value and not idx:
             string += "NONE"
             break