switch to equivalent str_to_bytes in py3compat

Chang She · Chang She · commit 866dc48cf614 · 2012-04-29T19:48:07.000-04:00
diff --git a/pandas/tseries/period.py b/pandas/tseries/period.py
@@ -529,7 +529,7 @@ def __new__(cls, data=None,
                 else:
                     base1, mult1 = _gfc(data.freq)
                     base2, mult2 = _gfc(freq)
-                    how = 'E'.encode('ascii') # Python 2.5 support
+                    how = py3compat.str_to_bytes('E')
                     data = lib.period_asfreq_arr(data.values, base1, mult1,
                                                  base2, mult2, how)
             else:
