use liboffsets to_offset function (#21693)

Author: jbrockmendel

pandas/_libs/tslib.pyx

@@ -51,6 +51,8 @@ from tslibs.conversion import tz_convert_single
 from tslibs.nattype import NaT, nat_strings, iNaT
 from tslibs.nattype cimport checknull_with_nat, NPY_NAT
 
+from tslibs.offsets cimport to_offset
+
 from tslibs.timestamps cimport (create_timestamp_from_ts,
                                 _NS_UPPER_BOUND, _NS_LOWER_BOUND)
 from tslibs.timestamps import Timestamp
@@ -118,7 +120,6 @@ def ints_to_pydatetime(ndarray[int64_t] arr, tz=None, freq=None,
         func_create = create_timestamp_from_ts
 
         if is_string_object(freq):
-            from pandas.tseries.frequencies import to_offset
             freq = to_offset(freq)
     elif box == "time":
         func_create = create_time_from_ts

pandas/_libs/tslibs/offsets.pxd

@@ -0,0 +1,3 @@
+# -*- coding: utf-8 -*-
+
+cdef to_offset(object obj)

pandas/_libs/tslibs/period.pyx

@@ -55,9 +55,9 @@ from parsing import parse_time_string, NAT_SENTINEL
 from resolution import Resolution
 from nattype import nat_strings, NaT, iNaT
 from nattype cimport _nat_scalar_rules, NPY_NAT
+from offsets cimport to_offset
 
 from pandas.tseries import offsets
-from pandas.tseries import frequencies
 
 
 cdef extern from "period_helper.h":
@@ -1015,7 +1015,7 @@ cdef class _Period(object):
             code, stride = get_freq_code(freq)
             freq = get_freq_str(code, stride)
 
-        freq = frequencies.to_offset(freq)
+        freq = to_offset(freq)
 
         if freq.n <= 0:
             raise ValueError('Frequency must be positive, because it'
@@ -1063,7 +1063,7 @@ cdef class _Period(object):
 
         if (PyDelta_Check(other) or util.is_timedelta64_object(other) or
                 isinstance(other, offsets.Tick)):
-            offset = frequencies.to_offset(self.freq.rule_code)
+            offset = to_offset(self.freq.rule_code)
             if isinstance(offset, offsets.Tick):
                 nanos = delta_to_nanoseconds(other)
                 offset_nanos = delta_to_nanoseconds(offset)

pandas/_libs/tslibs/timedeltas.pyx

@@ -33,6 +33,7 @@ from np_datetime cimport (cmp_scalar, reverse_ops, td64_to_tdstruct,
 
 from nattype import nat_strings, NaT
 from nattype cimport checknull_with_nat, NPY_NAT
+from offsets cimport to_offset
 
 # ----------------------------------------------------------------------
 # Constants
@@ -1050,7 +1051,6 @@ class Timedelta(_Timedelta):
         cdef:
             int64_t result, unit
 
-        from pandas.tseries.frequencies import to_offset
         unit = to_offset(freq).nanos
         result = unit * rounder(self.value / float(unit))
         return Timedelta(result, unit='ns')

pandas/_libs/tslibs/timestamps.pyx

@@ -30,6 +30,7 @@ from nattype cimport NPY_NAT
 from np_datetime import OutOfBoundsDatetime
 from np_datetime cimport (reverse_ops, cmp_scalar, check_dts_bounds,
                           pandas_datetimestruct, dt64_to_dtstruct)
+from offsets cimport to_offset
 from timedeltas import Timedelta
 from timedeltas cimport delta_to_nanoseconds
 from timezones cimport (
@@ -59,7 +60,6 @@ cdef inline object create_timestamp_from_ts(int64_t value,
 
 
 def round_ns(values, rounder, freq):
-
     """
     Applies rounding function at given frequency
 
@@ -73,8 +73,6 @@ def round_ns(values, rounder, freq):
     -------
     :obj:`ndarray`
     """
-
-    from pandas.tseries.frequencies import to_offset
     unit = to_offset(freq).nanos
 
     # GH21262 If the Timestamp is multiple of the freq str

setup.py

@@ -538,7 +538,8 @@ def pxd(name):
                      '_libs/tslibs/ccalendar',
                      '_libs/tslibs/timedeltas',
                      '_libs/tslibs/timezones',
-                     '_libs/tslibs/nattype'],
+                     '_libs/tslibs/nattype',
+                     '_libs/tslibs/offsets'],
         'depends': tseries_depends + ['pandas/_libs/src/period_helper.h'],
         'sources': np_datetime_sources + ['pandas/_libs/src/period_helper.c']},
     '_libs.properties': {
@@ -560,7 +561,8 @@ def pxd(name):
                      '_libs/tslibs/timedeltas',
                      '_libs/tslibs/timestamps',
                      '_libs/tslibs/timezones',
-                     '_libs/tslibs/nattype'],
+                     '_libs/tslibs/nattype',
+                     '_libs/tslibs/offsets'],
         'depends': tseries_depends,
         'sources': np_datetime_sources},
     '_libs.tslibs.ccalendar': {
@@ -619,7 +621,8 @@ def pxd(name):
     '_libs.tslibs.timedeltas': {
         'pyxfile': '_libs/tslibs/timedeltas',
         'pxdfiles': ['_libs/src/util',
-                     '_libs/tslibs/nattype'],
+                     '_libs/tslibs/nattype',
+                     '_libs/tslibs/offsets'],
         'depends': np_datetime_headers,
         'sources': np_datetime_sources},
     '_libs.tslibs.timestamps': {
@@ -628,6 +631,7 @@ def pxd(name):
                      '_libs/tslibs/ccalendar',
                      '_libs/tslibs/conversion',
                      '_libs/tslibs/nattype',
+                     '_libs/tslibs/offsets',
                      '_libs/tslibs/timedeltas',
                      '_libs/tslibs/timezones'],
         'depends': tseries_depends,