Date format issue

[snippsat]

Your error ValueError: time data '' show that your read of log_file return an empty string.

date = f.read() # return ''

Make the same error.

>>> date = ''
>>> datetime.strptime(date, "%Y-%m-%d")

Error:
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
  File "C:\python37\lib\_strptime.py", line 577, in _strptime_datetime
    tt, fraction, gmtoff_fraction = _strptime(data_string, format)
  File "C:\python37\lib\_strptime.py", line 359, in _strptime
    (data_string, format))
ValueError: time data '' does not match format '%Y-%m-%d'

With a date it work.

>>> date = '2019-03-11'
>>> datetime.strptime(date, "%Y-%m-%d")
datetime.datetime(2019, 3, 11, 0, 0)