data type mismatch error in from_json

[jkupka]

Right now to_json doesn´t ensure right data types and sometimes it´s not possible to load the saved network with from_json again.

The following example will raise a data type mismatch error because the reference apparent power will be saved as int instead as float and from_json is expecting sn_kva to be a float.

import pandapower as pp
import pandapower.networks as nw

net = nw.case9()
net.sn_kva = 1000
pp.to_json(net, "net.json")
net = pp.from_json("net.json")

[rbolgaryn]

Added test, rewritten the function to try to cast the data type first

[rbolgaryn]

we need to keep in mind that int(10.5) is 10

[rbolgaryn]

so net shouldn't have int fields

[rbolgaryn]

We shouldn't be casting types because we risk losing informatioon in a case like in my previous comment. If the user changes sn_kva to int, it is the responsibility of the user. We can discuss this on Monday, now I will make the pull request so that the above example works and net can be loaded from json.

[lthurner]

We shouldn't be casting types because we risk losing informatioon in a case like in my previous comment. If the user changes sn_kva to int, it is the responsibility of the user.

The task of the from_json / to_json functions should be to restore a grid exactly as it was saved, not to do data type checks or type casting. So if net.sn_kva is a string for some reason when to_json is applied, it should load again with net.sn_kva as a string.

I did not look into how the from_json / to_json functions were refactored, but if they expect certain data types in certain fields that is the wrong approach in my opinion. Maybe we need to roll back #139 and first discuss this more thoroughly?

edit: I understand with #154 no type casting is performed anymore and the net is restored as it is saved. So now from_json/to_json should work more robustly, good work @rbolgaryn

[jhmenke]

new from_json/to_json looks good. it is definitely cleaner than before.

one suggestion:

• add deprecationwarnings to from_json_string and from_json_dict in file_io.py, so that users know this function will be gone in the next releases