Use Mapping as a default SchemaNode typ.

[kotnik]

Typ of the Node should have a reasonable default, just like the documentation for _SchemaNode suggests.

[tseaver]

Thanks for the patch! I am +0 on the substance of the patch, but could you please back out the janitorial changes (the "Remove trailing whitespace" commit, I think) to make the bits being reviewed clearer?

[kotnik]

I have removed the irrelevant commit (my editor automatically removes the trailing garbage).

[jayd3e]

So the general consensus with this issue is that SchemaNode should always require a type in some form passed into it, b/c it is meant to be a lower level abstraction. MappingSchema/TupleSchema/SequenceSchema allow for this use-case, b/c you shouldn't have to pass the Mapping type to MappingSchema for example.

[mmerickel]

This should be an instance of Mapping. Specifically your options are:

@staticmethod
def schema_type():
    return Mapping()

or

schema_type = Mapping

[mmerickel]

This PR needs a test.

[kotnik]

Ok, I'll provide tests as well.

[mmerickel]

FWIW I think that SchemaNode should actually not have a default type and the docs be updated to reflect that. As this PR currently stands I think it will have no effect because the default type is still taken from the first argument to SchemaNode.__init__ (even if the first argument is another SchemaNode for use with the default mapping type).

[mmerickel]

We've decided to update the docs to indicate that the first parameter to SchemaNode is always the type and that there is no default so this patch is no longer necessary.