Try this :
html_source_code = requests.get("http://www.example.com/",
headers={'User-Agent':'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/44.0.2403.107 Safari/537.36',
'Upgrade-Insecure-Requests': '1',
'x-runtime': '148ms'},
allow_redirects=True).content