PERF: eliminate repeated get_option imports in period.pyx

Author: qwhelan

doc/source/whatsnew/v0.24.0.rst

@@ -1254,6 +1254,7 @@ Performance Improvements
 - Improved performance of :meth:`~DataFrame.where` for Categorical data (:issue:`24077`)
 - Improved performance of iterating over a :class:`Series`. Using :meth:`DataFrame.itertuples` now creates iterators
   without internally allocating lists of all elements (:issue:`20783`)
+- Improved performance of :class:`Period` constructor, additionally benefitting ``PeriodArray`` and ``PeriodIndex`` creation (:issue:`24084` and :issue:`24118`)
 
 .. _whatsnew_0240.docs:
 

pandas/_libs/tslibs/parsing.pyx

@@ -47,6 +47,20 @@ cdef set _not_datelike_strings = {'a', 'A', 'm', 'M', 'p', 'P', 't', 'T'}
 
 # ----------------------------------------------------------------------
 
+_get_option = None
+
+
+def get_option(param):
+    """ Defer import of get_option to break an import cycle that caused
+    significant performance degradation in Period construction. See
+    GH#24118 for details
+    """
+    global _get_option
+    if _get_option is None:
+        from pandas.core.config import get_option
+        _get_option = get_option
+    return _get_option(param)
+
 
 def parse_datetime_string(date_string, freq=None, dayfirst=False,
                           yearfirst=False, **kwargs):
@@ -117,7 +131,6 @@ def parse_time_string(arg, freq=None, dayfirst=None, yearfirst=None):
         freq = freq.rule_code
 
     if dayfirst is None or yearfirst is None:
-        from pandas.core.config import get_option
         if dayfirst is None:
             dayfirst = get_option("display.date_dayfirst")
         if yearfirst is None: