Cleaning: `with` statement can save your life

see https://gitlab.aip.de/lketzer/platypos/-/blob/master/platypos_package/Planet_class_LoFo14.py#L251

s = open(path_for_saving+"host_star_properties.txt", "w")
                star_params = "star_id,mass_star,radius_star,age,Lbol,Lx_age\n"\
                              + self.star_id + "," + str(self.mass_star) + ","\
                              + str(self.radius_star) + "," + str(self.age)\
                              + "," + str(self.Lbol/const.L_sun.cgs.value)\
                              + "," + str(self.Lx_age)
                s.write(star_params)
                s.close()

this is dangerous, because if you get an Error in the computation of star_params and you catch the Error the code won't close the file before the program stops. That is harmless as long as you have one file, wait to have 100, 1000 of files. All opened together, your laptop won't like it.

To prevent that you there were the old-fashion way (don't do it it is just to understand):

s = open(...)
try:
    star_params = compute(...)
    s.write(star_params)
except ValueError as exception:
    # LOG WARNING, ERROR What ever you want
    raise exception
finally:
    s.close()

This construction guaranty that even if you got an exception in the compute function the statement in finally will be called. That guaranty that the file will be closed what ever happens.

However this formulation was quite wordy and since python 2.x (what ever version, a long time ago anyway) the python developers added the with statement!

with open(...) as s:
    # compute

is equivalent to:

s = open(...)
try:
    s.__enter__()
    # compute
except:
    # treat exception
finally:
    s.__exit__()

s is a File object. File.__enter__() does nothing fancy, but File.__exit__() is nothing else than File.close() so you see much easier and shorter to use with and you get a full bench of improvements.