Krippendorff's alpha for two annotators with nominal data

gistfile1.txt

import pandas as pd

def calculate_Kalpha2(y1,y2):
    df = pd.concat([y1,y2], axis=1)
    df.columns = ['y1', 'y2']
    n = 2*len(df)
    agg = 0
    all = 0
    for label in df.y1.unique().tolist():
        agg += 2*len(df[(df.y1 == label) & (df.y2 == label)])
        asd = len(df[df.y1 == label]) + len(df[df.y2 == label])
        all += asd*(asd - 1)

    nom = (n-1)*agg - all
    denom = n*(n - 1) - all
    return nom/denom

#y1 and y2 are series. Annotations of two different annotators