code:

import requests
import json
import pandas as pd
import matplotlib.pyplot as plt
from io import BytesIO
import seaborn as sns

def getvoting():
    url = 'https://www.getvoting.org/NewData.json'
    raw = pd.DataFrame.from_dict(json.loads(requests.get(url).content.decode()), orient='index')

    mapping = {
        'Lab': 'Labour',
        'Lib Dem': 'Lib Dem',
        'Pledge': 'Pledge',
        'none': 'None'}
    return (raw.Reco
                .where(lambda s: s.isin(mapping), 'Other')
                .replace(mapping))

def current():
    url = 'https://data.london.gov.uk/download/general-election-results-2017/26ee40ae-becf-4839-bb0c-509024e61bfd/2017%2520General%2520Election%2520Results.xls'
    raw = pd.read_excel(BytesIO(requests.get(url).content))
    
    mapping = {
        'C': 'Conservative',
        'Lab': 'Labour',
        'SNP': 'SNP',
        'LD': 'Lib Dem'}
    return (raw
            .query('Year == 2017')
            .set_index('Code')
            ['Majority Party']
            .dropna()
            .where(lambda s: s.isin(mapping), 'Other')
            .replace(mapping))

joint = pd.concat({'current': current(), 'getvoting': getvoting()}, 1)
confusion = (joint
             .assign(dummy=1)
             .groupby(['current', 'getvoting'])
             .dummy.sum()
             .unstack()
             .fillna(0)
             .astype(int))