Merge pull request #3332 from jreback/period_perf2

PERF/CLN: infer Period in infer_dtype, later index inference is faster

Author: jreback

pandas/core/index.py

@@ -127,8 +127,8 @@ def __new__(cls, data, dtype=None, copy=False, name=None):
                     from pandas.tseries.index import DatetimeIndex
                     return DatetimeIndex(subarr, copy=copy, name=name)
 
-            if lib.is_period_array(subarr):
-                return PeriodIndex(subarr, name=name)
+                elif inferred == 'period':
+                    return PeriodIndex(subarr, name=name)
 
         subarr = subarr.view(cls)
         subarr.name = name

pandas/src/inference.pyx

@@ -97,6 +97,10 @@ def infer_dtype(object _values):
         if is_timedelta_or_timedelta64_array(values):
             return 'timedelta'
 
+    elif is_period(val):
+        if is_period_array(values):
+            return 'period'
+
     for i in range(n):
         val = util.get_value_1d(values, i)
         if util.is_integer_object(val):
@@ -321,6 +325,10 @@ def is_time_array(ndarray[object] values):
             return False
     return True
 
+def is_period(object o):
+    from pandas import Period
+    return isinstance(o,Period)
+
 def is_period_array(ndarray[object] values):
     cdef int i, n = len(values)
     from pandas import Period