Use TYPE_MAPPING from base_schema

[MartinAltmayer]

I ran the tests with Python 3.6.10, 3.7.7, and 3.8.1. I also tested this branch in my application which uses Python 3.8.1.

[lovasoa]

This looks good to me ! Could you just add one line in the README about this new feature ? Maybe in the Customizing the base Schema section.

[MartinAltmayer]

Thanks for merging! Shall I open a new PR for the README?

[MartinAltmayer]

Ok, I saw your own commit. Thanks for updating the README!

[lovasoa]

Yes, I updated the README. Thank you for your contribution @MartinAltmayer ! I am going to update the changelog and publish a new release.

[lovasoa]

Hmm... I'm thinking: my example may be super confusing.

class BaseSchema(marshmallow.Schema):
    TYPE_MAPPING = {CustomType: CustomField}

creates a schema where none of the default type mappings apply. This is probably never what anyone wants.

[lovasoa]

Should we update our code to use {**base_schema.TYPE_MAPPING, **Schema.TYPE_MAPPING}, or leave it like that, but change the documentation and the tests ?

[lovasoa]

I'd love to hear your opinion @sloria !

[lovasoa]

I implemented the first solution. I'll release it once I'm sure everyone agrees. @sloria , @MartinAltmayer ?

[MartinAltmayer]

Looks fine to me, the user probably never wants to remove the default mapping.

[lovasoa]

Ok, I'll publish that this weekend if no one opposes in the meantime.

[sloria]

Yeah, the implemented behavior seems reasonable to me

[lovasoa]

OK, it's deployed: https://pypi.org/project/marshmallow-dataclass/