REF: re-share Period methods (#46314)

Author: jbrockmendel

pandas/_libs/tslibs/dtypes.pxd

@@ -74,3 +74,5 @@ cdef enum PeriodDtypeCode:
 cdef class PeriodDtypeBase:
     cdef readonly:
         PeriodDtypeCode _dtype_code
+
+    cpdef int _get_to_timestamp_base(self)

pandas/_libs/tslibs/dtypes.pyi

@@ -16,6 +16,7 @@ class PeriodDtypeBase:
     def from_date_offset(cls, offset: BaseOffset) -> PeriodDtypeBase: ...
     @property
     def resolution(self) -> Resolution: ...
+    def _get_to_timestamp_base(self) -> int: ...
 
 class FreqGroup(Enum):
     FR_ANN: int

pandas/_libs/tslibs/dtypes.pyx

@@ -50,6 +50,25 @@ cdef class PeriodDtypeBase:
         code = offset._period_dtype_code
         return cls(code)
 
+    cpdef int _get_to_timestamp_base(self):
+        """
+        Return frequency code group used for base of to_timestamp against
+        frequency code.
+
+        Return day freq code against longer freq than day.
+        Return second freq code against hour between second.
+
+        Returns
+        -------
+        int
+        """
+        base = <c_FreqGroup>self._dtype_code
+        if base < FR_BUS:
+            return FR_DAY
+        elif FR_HR <= base <= FR_SEC:
+            return FR_SEC
+        return base
+
 
 _period_code_map = {
     # Annual freqs with various fiscal year ends.

pandas/_libs/tslibs/period.pyi

@@ -52,7 +52,14 @@ def period_ordinal(
 def freq_to_dtype_code(freq: BaseOffset) -> int: ...
 def validate_end_alias(how: str) -> Literal["E", "S"]: ...
 
-class Period:
+class PeriodMixin:
+    @property
+    def end_time(self) -> Timestamp: ...
+    @property
+    def start_time(self) -> Timestamp: ...
+    def _require_matching_freq(self, other, base: bool = ...) -> None: ...
+
+class Period(PeriodMixin):
     ordinal: int  # int64_t
     freq: BaseOffset
 
@@ -118,9 +125,5 @@ class Period:
     def month(self) -> int: ...
     @property
     def year(self) -> int: ...
-    @property
-    def end_time(self) -> Timestamp: ...
-    @property
-    def start_time(self) -> Timestamp: ...
     def __sub__(self, other) -> Period | BaseOffset: ...
     def __add__(self, other) -> Period: ...

pandas/_libs/tslibs/period.pyx

@@ -1545,25 +1545,6 @@ class IncompatibleFrequency(ValueError):
 cdef class PeriodMixin:
     # Methods shared between Period and PeriodArray
 
-    cpdef int _get_to_timestamp_base(self):
-        """
-        Return frequency code group used for base of to_timestamp against
-        frequency code.
-
-        Return day freq code against longer freq than day.
-        Return second freq code against hour between second.
-
-        Returns
-        -------
-        int
-        """
-        base = self._dtype._dtype_code
-        if base < FR_BUS:
-            return FR_DAY
-        elif FR_HR <= base <= FR_SEC:
-            return FR_SEC
-        return base
-
     @property
     def start_time(self) -> Timestamp:
         """
@@ -1861,7 +1842,7 @@ cdef class _Period(PeriodMixin):
             return endpoint - Timedelta(1, 'ns')
 
         if freq is None:
-            freq = self._get_to_timestamp_base()
+            freq = self._dtype._get_to_timestamp_base()
             base = freq
         else:
             freq = self._maybe_convert_freq(freq)

pandas/core/arrays/period.py

@@ -104,7 +104,7 @@ def f(self):
     return property(f)
 
 
-class PeriodArray(dtl.DatelikeOps):
+class PeriodArray(dtl.DatelikeOps, libperiod.PeriodMixin):
     """
     Pandas ExtensionArray for storing Period data.
 
@@ -500,7 +500,7 @@ def to_timestamp(self, freq=None, how: str = "start") -> DatetimeArray:
                 return (self + self.freq).to_timestamp(how="start") - adjust
 
         if freq is None:
-            freq = self._get_to_timestamp_base()
+            freq = self._dtype._get_to_timestamp_base()
             base = freq
         else:
             freq = Period._maybe_convert_freq(freq)
@@ -606,8 +606,7 @@ def asfreq(self, freq=None, how: str = "E") -> PeriodArray:
 
         freq = Period._maybe_convert_freq(freq)
 
-        # error: "BaseOffset" has no attribute "_period_dtype_code"
-        base1 = self.freq._period_dtype_code  # type: ignore[attr-defined]
+        base1 = self._dtype._dtype_code
         base2 = freq._period_dtype_code
 
         asi8 = self.asi8
@@ -884,56 +883,6 @@ def _check_timedeltalike_freq_compat(self, other):
 
         raise raise_on_incompatible(self, other)
 
-    # ------------------------------------------------------------------
-    # TODO: See if we can re-share this with Period
-
-    def _get_to_timestamp_base(self) -> int:
-        """
-        Return frequency code group used for base of to_timestamp against
-        frequency code.
-
-        Return day freq code against longer freq than day.
-        Return second freq code against hour between second.
-
-        Returns
-        -------
-        int
-        """
-        base = self._dtype._dtype_code
-        if base < FreqGroup.FR_BUS.value:
-            return FreqGroup.FR_DAY.value
-        elif FreqGroup.FR_HR.value <= base <= FreqGroup.FR_SEC.value:
-            return FreqGroup.FR_SEC.value
-        return base
-
-    @property
-    def start_time(self) -> DatetimeArray:
-        return self.to_timestamp(how="start")
-
-    @property
-    def end_time(self) -> DatetimeArray:
-        return self.to_timestamp(how="end")
-
-    def _require_matching_freq(self, other, base: bool = False) -> None:
-        # See also arrays.period.raise_on_incompatible
-        if isinstance(other, BaseOffset):
-            other_freq = other
-        else:
-            other_freq = other.freq
-
-        if base:
-            condition = self.freq.base != other_freq.base
-        else:
-            condition = self.freq != other_freq
-
-        if condition:
-            msg = DIFFERENT_FREQ.format(
-                cls=type(self).__name__,
-                own_freq=self.freqstr,
-                other_freq=other_freq.freqstr,
-            )
-            raise IncompatibleFrequency(msg)
-
 
 def raise_on_incompatible(left, right):
     """

pandas/tests/tseries/frequencies/test_freq_code.py

@@ -18,7 +18,7 @@ def test_get_to_timestamp_base(freqstr, exp_freqstr):
     per = Period._from_ordinal(1, off)
     exp_code = to_offset(exp_freqstr)._period_dtype_code
 
-    result_code = per._get_to_timestamp_base()
+    result_code = per._dtype._get_to_timestamp_base()
     assert result_code == exp_code