REF: make nat_strings cimport-able (pandas-dev#34105)

Author: jbrockmendel

pandas/_libs/tslib.pyx

@@ -50,8 +50,11 @@ from pandas._libs.tslibs.conversion cimport (
     _TSObject, convert_datetime_to_tsobject,
     get_datetime64_nanos)
 
-from pandas._libs.tslibs.nattype import nat_strings
-from pandas._libs.tslibs.nattype cimport NPY_NAT, c_NaT as NaT
+from pandas._libs.tslibs.nattype cimport (
+    NPY_NAT,
+    c_NaT as NaT,
+    c_nat_strings as nat_strings,
+)
 
 from pandas._libs.tslibs.offsets cimport to_offset
 

pandas/_libs/tslibs/__init__.py

@@ -3,6 +3,7 @@
     "NaT",
     "NaTType",
     "iNaT",
+    "nat_strings",
     "is_null_datetimelike",
     "OutOfBoundsDatetime",
     "IncompatibleFrequency",
@@ -17,7 +18,7 @@
 
 
 from .conversion import localize_pydatetime
-from .nattype import NaT, NaTType, iNaT, is_null_datetimelike
+from .nattype import NaT, NaTType, iNaT, is_null_datetimelike, nat_strings
 from .np_datetime import OutOfBoundsDatetime
 from .period import IncompatibleFrequency, Period
 from .timedeltas import Timedelta, delta_to_nanoseconds, ints_to_pytimedelta

pandas/_libs/tslibs/conversion.pyx

@@ -33,9 +33,12 @@ from pandas._libs.tslibs.timezones cimport (
 )
 from pandas._libs.tslibs.parsing import parse_datetime_string
 
-from pandas._libs.tslibs.nattype import nat_strings
 from pandas._libs.tslibs.nattype cimport (
-    NPY_NAT, checknull_with_nat, c_NaT as NaT)
+    NPY_NAT,
+    checknull_with_nat,
+    c_NaT as NaT,
+    c_nat_strings as nat_strings,
+)
 
 from pandas._libs.tslibs.tzconversion import tz_localize_to_utc
 from pandas._libs.tslibs.tzconversion cimport (

pandas/_libs/tslibs/nattype.pxd

@@ -4,7 +4,7 @@ from numpy cimport int64_t
 cdef int64_t NPY_NAT
 
 cdef bint _nat_scalar_rules[6]
-
+cdef set c_nat_strings
 
 cdef class _NaT(datetime):
     cdef readonly:

pandas/_libs/tslibs/nattype.pyx

@@ -35,6 +35,7 @@ from pandas._libs.tslibs.base cimport is_period_object
 # ----------------------------------------------------------------------
 # Constants
 nat_strings = {"NaT", "nat", "NAT", "nan", "NaN", "NAN"}
+cdef set c_nat_strings = nat_strings
 
 cdef int64_t NPY_NAT = util.get_nat()
 iNaT = NPY_NAT  # python-visible constant

pandas/_libs/tslibs/parsing.pyx

@@ -33,7 +33,10 @@ from dateutil.parser import parse as du_parse
 from pandas._config import get_option
 
 from pandas._libs.tslibs.ccalendar cimport c_MONTH_NUMBERS
-from pandas._libs.tslibs.nattype import nat_strings, NaT
+from pandas._libs.tslibs.nattype cimport (
+    c_nat_strings as nat_strings,
+    c_NaT as NaT,
+)
 from pandas._libs.tslibs.util cimport (
     is_array,
     is_offset_object,

pandas/_libs/tslibs/period.pyx

@@ -61,9 +61,13 @@ from pandas._libs.tslibs.frequencies cimport (
 )
 from pandas._libs.tslibs.parsing import parse_time_string
 from pandas._libs.tslibs.resolution import Resolution
-from pandas._libs.tslibs.nattype import nat_strings
 from pandas._libs.tslibs.nattype cimport (
-    _nat_scalar_rules, NPY_NAT, is_null_datetimelike, c_NaT as NaT)
+    _nat_scalar_rules,
+    NPY_NAT,
+    is_null_datetimelike,
+    c_NaT as NaT,
+    c_nat_strings as nat_strings,
+)
 from pandas._libs.tslibs.offsets cimport to_offset, is_tick_object
 from pandas._libs.tslibs.tzconversion cimport tz_convert_utc_to_tzlocal
 

pandas/_libs/tslibs/strptime.pyx

@@ -17,8 +17,11 @@ cimport cpython.datetime as datetime
 from pandas._libs.tslibs.np_datetime cimport (
     check_dts_bounds, dtstruct_to_dt64, npy_datetimestruct)
 
-from pandas._libs.tslibs.nattype cimport checknull_with_nat, NPY_NAT
-from pandas._libs.tslibs.nattype import nat_strings
+from pandas._libs.tslibs.nattype cimport (
+    checknull_with_nat,
+    NPY_NAT,
+    c_nat_strings as nat_strings,
+)
 
 cdef dict _parse_code_table = {'y': 0,
                                'Y': 1,

pandas/_libs/tslibs/timedeltas.pyx

@@ -28,9 +28,12 @@ from pandas._libs.tslibs.ccalendar cimport DAY_NANOS
 from pandas._libs.tslibs.np_datetime cimport (
     cmp_scalar, reverse_ops, td64_to_tdstruct, pandas_timedeltastruct)
 
-from pandas._libs.tslibs.nattype import nat_strings
 from pandas._libs.tslibs.nattype cimport (
-    checknull_with_nat, NPY_NAT, c_NaT as NaT)
+    checknull_with_nat,
+    NPY_NAT,
+    c_NaT as NaT,
+    c_nat_strings as nat_strings,
+)
 
 # ----------------------------------------------------------------------
 # Constants

pandas/core/tools/datetimes.py

@@ -936,7 +936,7 @@ def calc_with_mask(carg, mask):
 
     # string with NaN-like
     try:
-        mask = ~algorithms.isin(arg, list(tslib.nat_strings))
+        mask = ~algorithms.isin(arg, list(tslibs.nat_strings))
         return calc_with_mask(arg, mask)
     except (ValueError, OverflowError, TypeError):
         pass

pandas/tests/tslibs/test_api.py

@@ -29,6 +29,7 @@ def test_namespace():
         "NaTType",
         "iNaT",
         "is_null_datetimelike",
+        "nat_strings",
         "NullFrequencyError",
         "OutOfBoundsDatetime",
         "Period",