benchmark: make script py36 friendly

[VMois]

• replaces datetime.fromisoformat with datetime.strptime as former is not supported in py36

closes #569

[codecov-commenter]

Codecov Report

Merging #570 (0fd3b15) into master (b71b8d9) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #570   +/-   ##
=======================================
  Coverage   26.00%   26.00%           
=======================================
  Files          17       17           
  Lines        1546     1546           
=======================================
  Hits          402      402           
  Misses       1144     1144           

[mvidalgarcia]

I'm checking with both Python 3.8.12 and Python 3.6.8 using this script:

import time
from datetime import datetime

# datetime_format = "%Y-%m-%dT%H:%M:%S"

now = "2021-10-29T08:27:50"
f = lambda x: time.mktime(datetime.fromisoformat(x).timetuple())
# f = lambda x: int(time.mktime(datetime.strptime(x, datetime_format).timetuple()))

print(f(now))

To switch between before/after PR, un/comment all the lines

Before PR

3.8.12

$ python foo.py
1635488870

3.6.8

$ python foo.py
Traceback (most recent call last):
  File "foo.py", line 11, in <module>
    print(f(now))
  File "foo.py", line 8, in <lambda>
    f = lambda x: time.mktime(datetime.fromisoformat(x).timetuple())
AttributeError: type object 'datetime.datetime' has no attribute 'fromisoformat'

After PR

3.8.12

$ python foo.py
1635488870

3.6.8

$ python foo.py
1635488870

Works as expected 👍

PS. Need rebase.