Print which dois are broken

check-my-dois.py

import requests
import pybtex.database

with open('./ref.bib') as bibfile:
    bib_database = pybtex.database.parse_file(bibfile)

for key in bib_database.entries.keys():
    entry = bib_database.entries[key]
    if 'doi' in entry.fields:
        doi = entry.fields['doi'].replace('\_', '_')
        url = f'https://dx.doi.org/{doi}'
        response1 = requests.get(url)
        if response1.status_code != 200:
            alt_url = f'https://doi.org/{doi}'
            response2 = requests.get(alt_url)
            if response2.status_code != 200:
                if 'JSTOR' in response1.text or 'JSTOR' in response2.text:
                    print(f'{doi} is broken, but JSTOR maybe the reason')
                else:
                    print(f'{doi} is broken')