Hello,
sometimes the requests could not be completed correctly (may be due to DDOS or rate limit violation?), and apparently Poloniex responds with something that could not be parsed by your wrapper:

balances = self.polo.returnAvailableAccountBalances()

File "/home/strky/anaconda3/envs/py36/lib/python3.6/site-packages/poloniex/init.py", line 449, in returnAvailableAccountBalances
return self.call('returnAvailableAccountBalances')
File "/home/strky/anaconda3/envs/py36/lib/python3.6/site-packages/poloniex/retry.py", line 15, in wrapped
return function(*args, **kwargs)
File "/home/strky/anaconda3/envs/py36/lib/python3.6/site-packages/poloniex/init.py", line 175, in call
jsonout = _loads(ret.text, parse_float=str)
File "/home/strky/anaconda3/envs/py36/lib/python3.6/json/init.py", line 367, in loads
return cls(**kw).decode(s)
File "/home/strky/anaconda3/envs/py36/lib/python3.6/json/decoder.py", line 339, in decode
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
File "/home/strky/anaconda3/envs/py36/lib/python3.6/json/decoder.py", line 357, in raw_decode
raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Is it possible to wrap the json decoding into try/except and return the error with original text to aid troubleshooting?
Other solutions might be possible...