ValueError: Invalid type <class 'NoneType'>

[amotl]

Dear @sdispater and @frostming,

thanks a stack for conceiving and maintaining this excellent library. We just wanted to let you know about an issue we just discovered when serializing NoneType values [1]. We are aware that TOML does not know about any kinds of NULL values (toml-lang/toml#921).

This issue is merely a proposal to handle NoneType values gracefully by just ignoring them on serialization. The toml package does just that [2]. We have exercised the situation with all of toml, tomlkit, and tomli-w on behalf of a unit test at [3] and also reported the same issue to the author of tomli-w at hukkin/tomli-w#39.

With kind regards,
Andreas.

[1] isarengineering/SecPi#25
[2] isarengineering/SecPi#27
[3] https://gist.github.com/amotl/4d8bc928d781a5d0fbc7f404396f8417

[amotl]

We also found that, when using the access pattern to directly serialize to a file,

with open("testdrive.toml", "w") as config_file:
    tomlkit.dump(data, config_file)

tomlkit raises an exception, but still writes an empty file, when data contains any NoneType value. The test at [3] demonstrates it for easy reproduction.

[jcdrubay]

@amotl You are suggesting to ignore the NoneType values, and I suggest to keep them as a comment.

From toml specifications "Unspecified values are invalid.", but comments are.

For instance, this dictionary: {"a": 1, "b": None} would generate this string :

a = 1
# b = None

As a workaround, I strip the dictionary from empty values:

def stripper(data):
    """
    Workaround for:
    https://github.com/sdispater/tomlkit/issues/240
    """
    new_data = {}
    for k, v in data.items():
        if isinstance(v, dict):
            v = stripper(v)
        if v not in (u"", None, {}):
            new_data[k] = v
    return new_data

[jcdrubay]

Dear @amotl I have updated my previous reply to make it clearer. Sorry for this initial version that wasn't clear at all.

[frostming]

None type isn't supported by TOML spec and we are not going to do things beyond that. So no special handling, just as other parsers do. Closing it now