➜  ~ cat dt.py 
from datetime import *
dt = datetime.strptime('+1720', '%z')
print(dt)
➜  ~ python2 dt.py 
Traceback (most recent call last):
  File "dt.py", line 2, in <module>
    dt = datetime.strptime('+1720', '%z')
  File "/usr/lib/python2.7/_strptime.py", line 324, in _strptime
    (bad_directive, format))
ValueError: 'z' is a bad directive in format '%z'
➜  ~ python3 dt.py
1900-01-01 00:00:00+17:20

We should either mention it in doc, either cherry-pick the code from python3