[Python] tomlkit dump behaving different with same data

I have a small config which I define via dataclasses and then read from a toml to this datastructure. If the toml file does not exists I create one with default values. If in an update some new config parameters where added I would like to take the toml from the user location, take the existing entries and then add the new one an write the file again. Everything is working fine, accept for the adding the entries, here there there are some empty lines added in the file and i dont know why. I already checked - the dict input to the tomlkit.dump command is exactly the same - still the output differs. Has anyone an idea where this could come from?

This is my Dataclass (subclasses are not shown and should not matter):

@dataclass
class Config:
general: General = field(default_factory=General)
siemens: Siemens = field(default_factory=Siemens)
def dict(self):
return {k: v.dict() for k, v in self.__dict__.items()}

@classmethod
def load(cls, config_json):
return Config(general=General(**config_json['general']), siemens=Siemens(**config_json['siemens']))


this function adds missing keys (from the class) to the read toml file:

def put_dict_params_into_toml_doc(default: dict, params: TOMLDocument) -> bool:
params_missing = False
for key, value in default.items():
if isinstance(value, dict):
try:
child_params = params[key]
if put_dict_params_into_toml_doc(value, child_params):
params_missing = True
except KeyError:
print(f'using default "{value}" for "{key}" (not found in config params {params})')
params_missing = True
params[key] = value
else:
if key not in params:
print(f'using default "{value}" for "{key}" (not found in config params {params})')
params_missing = True
params[key] = value
return params_missing


this function removes params from the toml file which are not in the class (if new version doesnt need parameter anymore):

def remove_nonexisting_params(default: dict, params: any) -> any:
result = params.copy()
for key, value in params.items():
if isinstance(value, dict):
try:
child_params = default[key]
result[key] = remove_nonexisting_params(child_params, value)
except KeyError:
result.pop(key)
else:
if key not in default:
result.pop(key)
return result


Here the toml file get read - this part is working perfectly (when file does not exist it is written with default values):

def read_config(config_path:str) -> Config:
default_params = Config()
if os.path.exists(config_path):
with open(config_path, mode="rb") as fp:
config_params = tomlkit.load(fp)
params_missing = put_dict_params_into_toml_doc(default_params.dict(), config_params)
config_params = remove_nonexisting_params(default_params.dict(), config_params)
if params_missing:
write_config(config_path, Config.load(config_params))
else:
config_params = default_params.dict()
with open(config_path, mode="w") as fp:
tomlkit.dump(config_params, fp)
return Config.load(config_params)


Here the file should be written, when I use Config().dict() as config_params erverything is fine, only if in the missing_params path it adds some empty lines...

def write_config(config_path:str, config_params:Config):
with open(config_path, mode="w") as fp:
tomlkit.dump(config_params.dict(), fp)


Output when running when file does not exist:

[general]
test_ip_address = "x.x.x.x"
test_eth_port = "eth3"
duagon_ip_address = "x.x.x.x"
duagon_eth_port = "eth0"
logging_on = false
xml_outputfile = "TRDP.xml"

[siemens]
support_multiple_devices = true
stdv2_udev = [1]
smi_send = [[123], [123]]
smi_receive = [[123, 123]]


Output when one line is removed for test:

[general]
test_ip_address = "x.x.x.x"

test_eth_port = "eth3"

duagon_ip_address = "x.x.x.x"

duagon_eth_port = "eth0"

logging_on = false
xml_outputfile = "TRDP.xml"

[siemens]
support_multiple_devices = true
stdv2_udev = [1]

smi_send = [[123], [123]]

smi_receive = [[123, 123]]

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