REF: simplify tzconversion (pandas-dev#47019)

Author: jbrockmendel

pandas/_libs/tslibs/__init__.py

@@ -58,9 +58,7 @@
 )
 from pandas._libs.tslibs.timestamps import Timestamp
 from pandas._libs.tslibs.timezones import tz_compare
-from pandas._libs.tslibs.tzconversion import (
-    py_tz_convert_from_utc_single as tz_convert_from_utc_single,
-)
+from pandas._libs.tslibs.tzconversion import tz_convert_from_utc_single
 from pandas._libs.tslibs.vectorized import (
     dt64arr_to_periodarr,
     get_resolution,

pandas/_libs/tslibs/offsets.pyx

@@ -54,10 +54,7 @@ from pandas._libs.tslibs.ccalendar cimport (
     get_firstbday,
     get_lastbday,
 )
-from pandas._libs.tslibs.conversion cimport (
-    convert_datetime_to_tsobject,
-    localize_pydatetime,
-)
+from pandas._libs.tslibs.conversion cimport localize_pydatetime
 from pandas._libs.tslibs.nattype cimport (
     NPY_NAT,
     c_NaT as NaT,
@@ -68,7 +65,6 @@ from pandas._libs.tslibs.np_datetime cimport (
     npy_datetimestruct,
     pydate_to_dtstruct,
 )
-from pandas._libs.tslibs.tzconversion cimport tz_convert_from_utc_single
 
 from .dtypes cimport PeriodDtypeCode
 from .timedeltas cimport (
@@ -270,10 +266,8 @@ cdef _to_dt64D(dt):
     if getattr(dt, 'tzinfo', None) is not None:
         # Get the nanosecond timestamp,
         #  equiv `Timestamp(dt).value` or `dt.timestamp() * 10**9`
-        nanos = getattr(dt, "nanosecond", 0)
-        i8 = convert_datetime_to_tsobject(dt, tz=None, nanos=nanos).value
-        dt = tz_convert_from_utc_single(i8, dt.tzinfo)
-        dt = np.int64(dt).astype('datetime64[ns]')
+        naive = dt.astimezone(None)
+        dt = np.datetime64(naive, "D")
     else:
         dt = np.datetime64(dt)
     if dt.dtype.name != "datetime64[D]":

pandas/_libs/tslibs/timestamps.pyx

@@ -1979,22 +1979,19 @@ default 'raise'
             value = tz_localize_to_utc_single(self.value, tz,
                                               ambiguous=ambiguous,
                                               nonexistent=nonexistent)
-            out = Timestamp(value, tz=tz)
-            if out is not NaT:
-                out._set_freq(self._freq)  # avoid warning in constructor
-            return out
+        elif tz is None:
+            # reset tz
+            value = tz_convert_from_utc_single(self.value, self.tz)
+
         else:
-            if tz is None:
-                # reset tz
-                value = tz_convert_from_utc_single(self.value, self.tz)
-                out = Timestamp(value, tz=tz)
-                if out is not NaT:
-                    out._set_freq(self._freq)  # avoid warning in constructor
-                return out
-            else:
-                raise TypeError(
-                    "Cannot localize tz-aware Timestamp, use tz_convert for conversions"
-                )
+            raise TypeError(
+                "Cannot localize tz-aware Timestamp, use tz_convert for conversions"
+            )
+
+        out = Timestamp(value, tz=tz)
+        if out is not NaT:
+            out._set_freq(self._freq)  # avoid warning in constructor
+        return out
 
     def tz_convert(self, tz):
         """

pandas/_libs/tslibs/tzconversion.pxd

@@ -6,8 +6,8 @@ from numpy cimport (
 )
 
 
-cdef int64_t tz_convert_from_utc_single(
-    int64_t utc_val, tzinfo tz, bint* fold=?, Py_ssize_t* outpos=?
+cpdef int64_t tz_convert_from_utc_single(
+    int64_t utc_val, tzinfo tz
 ) except? -1
 cdef int64_t tz_localize_to_utc_single(
     int64_t val, tzinfo tz, object ambiguous=*, object nonexistent=*

pandas/_libs/tslibs/tzconversion.pyi

@@ -8,8 +8,8 @@ import numpy as np
 
 from pandas._typing import npt
 
-# py_tz_convert_from_utc_single exposed for testing
-def py_tz_convert_from_utc_single(val: np.int64, tz: tzinfo) -> np.int64: ...
+# tz_convert_from_utc_single exposed for testing
+def tz_convert_from_utc_single(val: np.int64, tz: tzinfo) -> np.int64: ...
 def tz_localize_to_utc(
     vals: npt.NDArray[np.int64],
     tz: tzinfo | None,

pandas/_libs/tslibs/tzconversion.pyx

@@ -183,29 +183,28 @@ timedelta-like}
     localized : ndarray[int64_t]
     """
     cdef:
-        const int64_t[::1] deltas
         ndarray[uint8_t, cast=True] ambiguous_array
-        Py_ssize_t i, idx, pos, ntrans, n = vals.shape[0]
+        Py_ssize_t i, idx, pos, n = vals.shape[0]
         Py_ssize_t delta_idx_offset, delta_idx, pos_left, pos_right
-        int64_t *tdata
         int64_t v, left, right, val, new_local, remaining_mins
         int64_t first_delta, delta
         int64_t shift_delta = 0
-        ndarray[int64_t] trans, result_a, result_b, dst_hours
+        ndarray[int64_t] result_a, result_b, dst_hours
         int64_t[::1] result
         npy_datetimestruct dts
         bint infer_dst = False, is_dst = False, fill = False
         bint shift_forward = False, shift_backward = False
         bint fill_nonexist = False
         str stamp
+        Localizer info = Localizer(tz)
 
     # Vectorized version of DstTzInfo.localize
-    if is_utc(tz) or tz is None:
+    if info.use_utc:
         return vals.copy()
 
     result = cnp.PyArray_EMPTY(vals.ndim, vals.shape, cnp.NPY_INT64, 0)
 
-    if is_tzlocal(tz) or is_zoneinfo(tz):
+    if info.use_tzlocal:
         for i in range(n):
             v = vals[i]
             if v == NPY_NAT:
@@ -214,9 +213,8 @@ timedelta-like}
                 result[i] = v - _tz_localize_using_tzinfo_api(v, tz, to_utc=True)
         return result.base  # to return underlying ndarray
 
-    elif is_fixed_offset(tz):
-        _, deltas, _ = get_dst_info(tz)
-        delta = deltas[0]
+    elif info.use_fixed:
+        delta = info.delta
         for i in range(n):
             v = vals[i]
             if v == NPY_NAT:
@@ -259,14 +257,9 @@ timedelta-like}
                "shift_backwards} or a timedelta object")
         raise ValueError(msg)
 
-    trans, deltas, _ = get_dst_info(tz)
-
-    tdata = <int64_t*>cnp.PyArray_DATA(trans)
-    ntrans = trans.shape[0]
-
     # Determine whether each date lies left of the DST transition (store in
     # result_a) or right of the DST transition (store in result_b)
-    result_a, result_b =_get_utc_bounds(vals, tdata, ntrans, deltas)
+    result_a, result_b =_get_utc_bounds(vals, info.tdata, info.ntrans, info.deltas)
 
     # silence false-positive compiler warning
     dst_hours = np.empty(0, dtype=np.int64)
@@ -278,7 +271,7 @@ timedelta-like}
     # Shift the delta_idx by if the UTC offset of
     # the target tz is greater than 0 and we're moving forward
     # or vice versa
-    first_delta = deltas[0]
+    first_delta = info.deltas[0]
     if (shift_forward or shift_delta > 0) and first_delta > 0:
         delta_idx_offset = 1
     elif (shift_backward or shift_delta < 0) and first_delta < 0:
@@ -336,10 +329,10 @@ timedelta-like}
                     # nonexistent times
                     new_local = val - remaining_mins - 1
 
-                delta_idx = bisect_right_i8(tdata, new_local, ntrans)
+                delta_idx = bisect_right_i8(info.tdata, new_local, info.ntrans)
 
                 delta_idx = delta_idx - delta_idx_offset
-                result[i] = new_local - deltas[delta_idx]
+                result[i] = new_local - info.deltas[delta_idx]
             elif fill_nonexist:
                 result[i] = NPY_NAT
             else:
@@ -519,19 +512,7 @@ cdef ndarray[int64_t] _get_dst_hours(
 # ----------------------------------------------------------------------
 # Timezone Conversion
 
-def py_tz_convert_from_utc_single(int64_t utc_val, tzinfo tz):
-    # The 'bint* fold=NULL' in tz_convert_from_utc_single means we cannot
-    #  make it cdef, so this is version exposed for testing from python.
-    return tz_convert_from_utc_single(utc_val, tz)
-
-
-@cython.boundscheck(False)
-cdef int64_t tz_convert_from_utc_single(
-    int64_t utc_val,
-    tzinfo tz,
-    bint* fold=NULL,
-    Py_ssize_t* outpos=NULL,
-) except? -1:
+cpdef int64_t tz_convert_from_utc_single(int64_t utc_val, tzinfo tz) except? -1:
     """
     Convert the val (in i8) from UTC to tz
 
@@ -541,8 +522,6 @@ cdef int64_t tz_convert_from_utc_single(
     ----------
     utc_val : int64
     tz : tzinfo
-    fold : bint*, default NULL
-    outpos : Py_ssize_t*, default NULL
 
     Returns
     -------
@@ -552,13 +531,8 @@ cdef int64_t tz_convert_from_utc_single(
         Localizer info = Localizer(tz)
         Py_ssize_t pos
 
-    if utc_val == NPY_NAT:
-        return utc_val
-
-    if outpos is not NULL and info.use_pytz:
-        return info.utc_val_to_local_val(utc_val, outpos, fold)
-    else:
-        return info.utc_val_to_local_val(utc_val, &pos, fold)
+    # Note: caller is responsible for ensuring utc_val != NPY_NAT
+    return info.utc_val_to_local_val(utc_val, &pos)
 
 
 # OSError may be thrown by tzlocal on windows at or close to 1970-01-01

pandas/tests/tslibs/test_conversion.py

@@ -22,7 +22,7 @@
 
 def _compare_utc_to_local(tz_didx):
     def f(x):
-        return tzconversion.py_tz_convert_from_utc_single(x, tz_didx.tz)
+        return tzconversion.tz_convert_from_utc_single(x, tz_didx.tz)
 
     result = tz_convert_from_utc(tz_didx.asi8, tz_didx.tz)
     expected = np.vectorize(f)(tz_didx.asi8)