refactor name method of PeriodDtype, refactor __arrow_array__ and add test for ValueError in test_period.py

Author: natmokval

pandas/_libs/tslibs/period.pyx

@@ -1544,7 +1544,6 @@ def extract_ordinals(ndarray values, freq) -> np.ndarray:
         # if we don't raise here, we'll segfault later!
         raise TypeError("extract_ordinals values must be object-dtype")
 
-    freqstr = Period._maybe_convert_freq(freq).freqstr
     freqstr = freq_to_period_freqstr(freq.n, freq.name)
 
     for i in range(n):

pandas/core/arrays/period.py

@@ -37,6 +37,7 @@
 from pandas._libs.tslibs.dtypes import (
     OFFSET_TO_PERIOD_FREQSTR,
     FreqGroup,
+    freq_to_period_freqstr,
 )
 from pandas._libs.tslibs.fields import isleapyear_arr
 from pandas._libs.tslibs.offsets import (
@@ -412,10 +413,7 @@ def __arrow_array__(self, type=None):
                     f"Not supported to convert PeriodArray to '{type}' type"
                 )
 
-        if self.freqstr == "ME":
-            period_type = ArrowPeriodType("M")
-        else:
-            period_type = ArrowPeriodType(self.freqstr)
+        period_type = ArrowPeriodType(freq_to_period_freqstr(1, self.freqstr))
         storage_array = pyarrow.array(self._ndarray, mask=self.isna(), type="int64")
         return pyarrow.ExtensionArray.from_storage(period_type, storage_array)
 

pandas/core/dtypes/dtypes.py

@@ -42,6 +42,7 @@
 from pandas._libs.tslibs.dtypes import (
     PeriodDtypeBase,
     abbrev_to_npy_unit,
+    freq_to_period_freqstr,
 )
 from pandas.compat import pa_version_under7p0
 from pandas.errors import PerformanceWarning
@@ -999,8 +1000,7 @@ def __str__(self) -> str_type:
 
     @property
     def name(self) -> str_type:
-        dname = {"ME": "period[M]"}
-        return dname.get(self._freqstr, f"period[{self._freqstr}]")
+        return "".join(["period[", freq_to_period_freqstr(1, self._freqstr), "]"])
 
     @property
     def na_value(self) -> NaTType:

pandas/tests/scalar/period/test_period.py

@@ -1590,3 +1590,9 @@ def test_invalid_frequency_error_message():
     msg = "Invalid frequency: <WeekOfMonth: week=0, weekday=0>"
     with pytest.raises(ValueError, match=msg):
         Period("2012-01-02", freq="WOM-1MON")
+
+
+def test_invalid_frequency_period_error_message():
+    msg = "Invalid frequency: ME"
+    with pytest.raises(ValueError, match=msg):
+        Period("2012-01-02", freq="ME")