REF: implement ParseState (#55617)

* REF: implement ParseState

* REF: inline convert_timezone

* ParseState->DatetimeParseState

Author: jbrockmendel

pandas/_libs/tslib.pyx

@@ -46,7 +46,10 @@ from pandas._libs.tslibs.np_datetime cimport (
 import_pandas_datetime()
 
 
-from pandas._libs.tslibs.strptime cimport parse_today_now
+from pandas._libs.tslibs.strptime cimport (
+    DatetimeParseState,
+    parse_today_now,
+)
 from pandas._libs.util cimport (
     is_float_object,
     is_integer_object,
@@ -58,7 +61,6 @@ from pandas._libs.tslibs.conversion cimport (
     _TSObject,
     cast_from_unit,
     convert_str_to_tsobject,
-    convert_timezone,
     get_datetime64_nanos,
     parse_pydatetime,
 )
@@ -454,9 +456,9 @@ cpdef array_to_datetime(
         float tz_offset
         set out_tzoffset_vals = set()
         tzinfo tz_out = None
-        bint found_tz = False, found_naive = False
         cnp.flatiter it = cnp.PyArray_IterNew(values)
         NPY_DATETIMEUNIT creso = NPY_FR_ns
+        DatetimeParseState state = DatetimeParseState()
 
     # specify error conditions
     assert is_raise or is_ignore or is_coerce
@@ -474,17 +476,7 @@ cpdef array_to_datetime(
                 iresult[i] = NPY_NAT
 
             elif PyDateTime_Check(val):
-                if val.tzinfo is not None:
-                    found_tz = True
-                else:
-                    found_naive = True
-                tz_out = convert_timezone(
-                    val.tzinfo,
-                    tz_out,
-                    found_naive,
-                    found_tz,
-                    utc_convert,
-                )
+                tz_out = state.process_datetime(val, tz_out, utc_convert)
                 iresult[i] = parse_pydatetime(val, &dts, utc_convert, creso=creso)
 
             elif PyDate_Check(val):

pandas/_libs/tslibs/conversion.pxd

@@ -47,13 +47,6 @@ cpdef (int64_t, int) precision_from_unit(str unit, NPY_DATETIMEUNIT out_reso=*)
 
 cdef maybe_localize_tso(_TSObject obj, tzinfo tz, NPY_DATETIMEUNIT reso)
 
-cdef tzinfo convert_timezone(
-    tzinfo tz_in,
-    tzinfo tz_out,
-    bint found_naive,
-    bint found_tz,
-    bint utc_convert,
-)
 
 cdef int64_t parse_pydatetime(
     datetime val,

pandas/_libs/tslibs/conversion.pyx

@@ -673,59 +673,6 @@ cpdef inline datetime localize_pydatetime(datetime dt, tzinfo tz):
     return _localize_pydatetime(dt, tz)
 
 
-cdef tzinfo convert_timezone(
-    tzinfo tz_in,
-    tzinfo tz_out,
-    bint found_naive,
-    bint found_tz,
-    bint utc_convert,
-):
-    """
-    Validate that ``tz_in`` can be converted/localized to ``tz_out``.
-
-    Parameters
-    ----------
-    tz_in : tzinfo or None
-        Timezone info of element being processed.
-    tz_out : tzinfo or None
-        Timezone info of output.
-    found_naive : bool
-        Whether a timezone-naive element has been found so far.
-    found_tz : bool
-        Whether a timezone-aware element has been found so far.
-    utc_convert : bool
-        Whether to convert/localize to UTC.
-
-    Returns
-    -------
-    tz_info
-        Timezone info of output.
-
-    Raises
-    ------
-    ValueError
-        If ``tz_in`` can't be converted/localized to ``tz_out``.
-    """
-    if tz_in is not None:
-        if utc_convert:
-            pass
-        elif found_naive:
-            raise ValueError("Tz-aware datetime.datetime "
-                             "cannot be converted to "
-                             "datetime64 unless utc=True")
-        elif tz_out is not None and not tz_compare(tz_out, tz_in):
-            raise ValueError("Tz-aware datetime.datetime "
-                             "cannot be converted to "
-                             "datetime64 unless utc=True")
-        else:
-            tz_out = tz_in
-    else:
-        if found_tz and not utc_convert:
-            raise ValueError("Cannot mix tz-aware with "
-                             "tz-naive values")
-    return tz_out
-
-
 cdef int64_t parse_pydatetime(
     datetime val,
     npy_datetimestruct *dts,

pandas/_libs/tslibs/strptime.pxd

@@ -1,4 +1,16 @@
+from cpython.datetime cimport (
+    datetime,
+    tzinfo,
+)
 from numpy cimport int64_t
 
 
 cdef bint parse_today_now(str val, int64_t* iresult, bint utc)
+
+
+cdef class DatetimeParseState:
+    cdef:
+        bint found_tz
+        bint found_naive
+
+    cdef tzinfo process_datetime(self, datetime dt, tzinfo tz, bint utc_convert)

pandas/_libs/tslibs/strptime.pyx

@@ -48,10 +48,7 @@ from numpy cimport (
 )
 
 from pandas._libs.missing cimport checknull_with_nat_and_na
-from pandas._libs.tslibs.conversion cimport (
-    convert_timezone,
-    get_datetime64_nanos,
-)
+from pandas._libs.tslibs.conversion cimport get_datetime64_nanos
 from pandas._libs.tslibs.nattype cimport (
     NPY_NAT,
     c_nat_strings as nat_strings,
@@ -73,6 +70,7 @@ import_pandas_datetime()
 from pandas._libs.tslibs.np_datetime import OutOfBoundsDatetime
 
 from pandas._libs.tslibs.timestamps cimport _Timestamp
+from pandas._libs.tslibs.timezones cimport tz_compare
 from pandas._libs.util cimport (
     is_float_object,
     is_integer_object,
@@ -156,6 +154,37 @@ cdef dict _parse_code_table = {"y": 0,
                                "u": 22}
 
 
+cdef class DatetimeParseState:
+    def __cinit__(self):
+        self.found_tz = False
+        self.found_naive = False
+
+    cdef tzinfo process_datetime(self, datetime dt, tzinfo tz, bint utc_convert):
+        if dt.tzinfo is not None:
+            self.found_tz = True
+        else:
+            self.found_naive = True
+
+        if dt.tzinfo is not None:
+            if utc_convert:
+                pass
+            elif self.found_naive:
+                raise ValueError("Tz-aware datetime.datetime "
+                                 "cannot be converted to "
+                                 "datetime64 unless utc=True")
+            elif tz is not None and not tz_compare(tz, dt.tzinfo):
+                raise ValueError("Tz-aware datetime.datetime "
+                                 "cannot be converted to "
+                                 "datetime64 unless utc=True")
+            else:
+                tz = dt.tzinfo
+        else:
+            if self.found_tz and not utc_convert:
+                raise ValueError("Cannot mix tz-aware with "
+                                 "tz-naive values")
+        return tz
+
+
 def array_strptime(
     ndarray[object] values,
     str fmt,
@@ -183,13 +212,12 @@ def array_strptime(
         bint is_raise = errors=="raise"
         bint is_ignore = errors=="ignore"
         bint is_coerce = errors=="coerce"
-        bint found_naive = False
-        bint found_tz = False
         tzinfo tz_out = None
         bint iso_format = format_is_iso(fmt)
         NPY_DATETIMEUNIT out_bestunit
         int out_local = 0, out_tzoffset = 0
         bint string_to_dts_succeeded = 0
+        DatetimeParseState state = DatetimeParseState()
 
     assert is_raise or is_ignore or is_coerce
 
@@ -276,17 +304,7 @@ def array_strptime(
                 iresult[i] = NPY_NAT
                 continue
             elif PyDateTime_Check(val):
-                if val.tzinfo is not None:
-                    found_tz = True
-                else:
-                    found_naive = True
-                tz_out = convert_timezone(
-                    val.tzinfo,
-                    tz_out,
-                    found_naive,
-                    found_tz,
-                    utc,
-                )
+                tz_out = state.process_datetime(val, tz_out, utc)
                 if isinstance(val, _Timestamp):
                     iresult[i] = val.tz_localize(None).as_unit("ns")._value
                 else: