CLN: remove usages of base_and_stride (#34700)

Author: jbrockmendel

pandas/_libs/tslibs/offsets.pyx

@@ -3491,7 +3491,7 @@ INVALID_FREQ_ERR_MSG = "Invalid frequency: {0}"
 _offset_map = {}
 
 
-cpdef base_and_stride(str freqstr):
+cdef _base_and_stride(str freqstr):
     """
     Return base freq and stride info from string representation
 
@@ -3502,7 +3502,7 @@ cpdef base_and_stride(str freqstr):
 
     Examples
     --------
-    _freq_and_stride('5Min') -> 'Min', 5
+    _base_and_stride('5Min') -> 'Min', 5
     """
     groups = opattern.match(freqstr)
 
@@ -3606,7 +3606,7 @@ cpdef to_offset(freq):
         stride = freq[1]
         if isinstance(stride, str):
             name, stride = stride, name
-        name, _ = base_and_stride(name)
+        name, _ = _base_and_stride(name)
         delta = _get_offset(name) * stride
 
     elif isinstance(freq, timedelta):

pandas/core/arrays/datetimes.py

@@ -12,7 +12,6 @@
     conversion,
     fields,
     iNaT,
-    offsets as liboffsets,
     resolution as libresolution,
     timezones,
     to_offset,
@@ -1106,8 +1105,7 @@ def to_period(self, freq=None):
 
             #  https://github.com/pandas-dev/pandas/issues/33358
             if res is None:
-                base, stride = liboffsets.base_and_stride(freq)
-                res = f"{stride}{base}"
+                res = freq
 
             freq = res
 

pandas/plotting/_matplotlib/timeseries.py

@@ -7,7 +7,6 @@
 
 from pandas._libs.tslibs import Period, to_offset
 from pandas._libs.tslibs.frequencies import FreqGroup
-from pandas._libs.tslibs.offsets import base_and_stride
 from pandas._typing import FrameOrSeriesUnion
 
 from pandas.core.dtypes.generic import (
@@ -167,12 +166,9 @@ def _get_ax_freq(ax):
 
 
 def _get_period_alias(freq) -> Optional[str]:
-    if isinstance(freq, DateOffset):
-        freq = freq.rule_code
-    else:
-        freq = base_and_stride(freq)[0]
+    freqstr = to_offset(freq).rule_code
 
-    freq = get_period_alias(freq)
+    freq = get_period_alias(freqstr)
     return freq