rare count by column

gistfile1.txt

from csv import DictReader
import numpy as np
import pandas as pd


class NestedDictCreator(dict):
    """
    Implementation of perl's autovivification feature.
    Used to generate nested dictionaries on the fly
    """
    def __getitem__(self, item):
        try:
            return dict.__getitem__(self, item)
        except KeyError:
            value = self[item] = type(self)()
            return value

categoric = ["C" + str(x) for x in range(1, 27)]
category_counts = NestedDictCreator()

for idx, x in enumerate(range(15, 15+len(categoric))):
    train = pd.read_csv('train.csv', header=0, usecols=[x])
    category_counts[categoric[idx]] = {key: value for (key, value) in
                                       dict(train[categoric[idx]].value_counts()).iteritems() if value == 1}
    print "col %s complete" % categoric[idx]