from simple_salesforce import Salesforce

sf = Salesforce(username='xxx', password='yyy', security_token='zzz')

query_res = sf.query_all('select variable from table')

...
  File "C:Python27libjson__init__.py", line 351, in loads
    return cls(encoding=encoding, **kw).decode(s)
  File "C:Python27libjsondecoder.py", line 365, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "C:Python27libjsondecoder.py", line 383, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded