This is just a little bit of maintenance, as I'm wading through the code.
This MR cleans
It was tested so:
In [1]: from cal_tools.tools import get_dir_creation_date
In [2]: folder = "/gpfs/exfel/exp/DETLAB/202031/p900172/raw"
In [3]: get_dir_creation_date(folder, 10)
Out[3]: datetime.datetime(2020, 7, 20, 12, 39, 20, 631633)
In [4]: get_dir_creation_date(folder, 4) # no such run, None is returned
In [5]: One question maybe is, should this function return None when the date could not be extracted, as it is now, or to raise?
I'd prefer to raise an error, so that it's clear that this step failed, rather than failing later.