str() takes at most 1 argument (2 given)

[echo-bravo-yahoo]

$ tasktime.py personal

Configuration override rc.json.array:on
Traceback (most recent call last):
File "tasktime.py", line 219, in
c.create_statistic(project)
File "tasktime.py", line 54, in create_statistic
json_str=str(json_tmp, encoding="utf8")
TypeError: str() takes at most 1 argument (2 given)

[echo-bravo-yahoo]

$ python --version
Python 2.7.13
$ task --version
2.5.1