PyPi provides a JSON endpoint with package metadata:
>>> import requests
>>> url="https://pypi.org/pypi/{}/json"
>>> json = requests.get(url.format('pandas')).json()
>>> json['info']['requires_dist']
['numpy (>=1.9.0)', 'pytz (>=2011k)', 'python-dateutil (>=2.5.0)']
>>> json['info']['requires_python']
'>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*'
For a specific package version, add an additional version segment to the URL:
https://pypi.org/pypi/pandas/0.22.0/json