CLN: small clean-up PeriodIndex (easy parts of #23416)

Author: jbrockmendel

pandas/core/arrays/datetimelike.py

@@ -944,6 +944,9 @@ def validate_dtype_freq(dtype, freq):
     ValueError : non-period dtype
     IncompatibleFrequency : mismatch between dtype and freq
     """
+    if freq is not None:
+        freq = frequencies.to_offset(freq)
+
     if dtype is not None:
         dtype = pandas_dtype(dtype)
         if not is_period_dtype(dtype):

pandas/core/indexes/period.py

@@ -29,7 +29,7 @@
 from pandas._libs.tslibs import resolution
 
 from pandas.core.algorithms import unique1d
-from pandas.core.dtypes.dtypes import PeriodDtype
+import pandas.core.arrays.datetimelike as dtl
 from pandas.core.arrays.period import PeriodArray, period_array
 from pandas.core.base import _shared_docs
 from pandas.core.indexes.base import _index_shared_docs, ensure_index
@@ -48,17 +48,6 @@
     dict(target_klass='PeriodIndex or list of Periods'))
 
 
-def _wrap_field_accessor(name):
-    fget = getattr(PeriodArray, name).fget
-
-    def f(self):
-        result = fget(self)
-        return Index(result, name=self.name)
-
-    f.__name__ = name
-    f.__doc__ = fget.__doc__
-    return property(f)
-
 # --- Period index sketch
 
 
@@ -211,27 +200,11 @@ def __new__(cls, data=None, ordinal=None, freq=None, start=None, end=None,
 
         if data is None and ordinal is None:
             # range-based.
-            if periods is not None:
-                if is_float(periods):
-                    periods = int(periods)
-
-                elif not is_integer(periods):
-                    msg = 'periods must be a number, got {periods}'
-                    raise TypeError(msg.format(periods=periods))
-
             data, freq = PeriodArray._generate_range(start, end, periods,
                                                      freq, fields)
             data = PeriodArray(data, freq=freq)
         else:
-            if freq is None and dtype is not None:
-                freq = PeriodDtype(dtype).freq
-            elif freq and dtype:
-                freq = PeriodDtype(freq).freq
-                dtype = PeriodDtype(dtype).freq
-
-                if freq != dtype:
-                    msg = "specified freq and dtype are different"
-                    raise IncompatibleFrequency(msg)
+            freq = dtl.validate_dtype_freq(dtype, freq)
 
             # PeriodIndex allow PeriodIndex(period_index, freq=different)
             # Let's not encourage that kind of behavior in PeriodArray.