Merge branch 'master' of https://github.com/pandas-dev/pandas into ts…

…libs-resolution

pandas/_libs/period.pyx

@@ -27,14 +27,16 @@ from util cimport is_period_object, is_string_object, INT32_MIN
 
 from lib cimport is_null_datetimelike
 from pandas._libs import tslib
-from pandas._libs.tslib import Timestamp, iNaT, NaT
+from pandas._libs.tslib import Timestamp, iNaT
 from tslibs.timezones cimport (
     is_utc, is_tzlocal, get_utcoffset, get_dst_info, maybe_get_tz)
 
 from tslibs.parsing import (parse_time_string, NAT_SENTINEL,
-                            _get_rule_month, _MONTH_NUMBERS, _nat_strings)
+                            _get_rule_month, _MONTH_NUMBERS)
 from tslibs.frequencies cimport get_freq_code
 from tslibs.resolution import resolution, Resolution
+from tslibs.nattype import nat_strings, NaT
+from tslibs.nattype cimport _nat_scalar_rules
 
 from pandas.tseries import offsets
 from pandas.tseries import frequencies
@@ -1080,7 +1082,7 @@ class Period(_Period):
                 converted = other.asfreq(freq)
                 ordinal = converted.ordinal
 
-        elif is_null_datetimelike(value) or value in _nat_strings:
+        elif is_null_datetimelike(value) or value in nat_strings:
             ordinal = iNaT
 
         elif is_string_object(value) or util.is_integer_object(value):