import pandas as pd;
print("version",pd.__version__)
date_interval = pd.interval_range(pd.Timestamp('2018-01-01'), freq='3D', periods=3)
pi = pd.period_range('2018-01-05', freq='D', periods=3)
array = date_interval.get_indexer(pi)
array1 = date_interval.get_indexer(pd.array(pi))
array3 = date_interval.get_indexer(list(pi))
array4 = date_interval.get_indexer(list(pi) + [10])
output = date_interval.get_indexer(list(pi.astype(str)))
print("Proper output", output)