Recursive loading trouble for immutables

[Mel]

rekkufa wrote:
> I am currently building a system for serializing python objects
 > to a readable file-format, as well as creating python objects by
 > parsing the same format. It is more or less complete except for
 > a single issue I just cannot figure out by myself: How to load
 > data that specifies immutables that recursively reference
 > themselves.
> 
> There are only a few solutions I can think of.
> 
> One: While loading recursive objects, I always create empty versions
 > of objects (lists, dicts, classes) etc, and fill them in afterwards.
 > This works fine for loading recursive lists and such, but as
 > immutables are, well, immutable, this gets me nowhere with important
 > datatypes like tuples.
> [ ... ]

I can imagine a C function that might do it.
If it were a list, of course, a Python function would be easy:

def IdioList (contents, marker):
     t = []
     t[:] = [x if x is not marker else t for x in contents]
     return t

With tuples, by the time we have the tuple's identity it's too late,
but I suspect that in C we could bend the rules enough.
The marker would be a caller-supplied object with the property that 
the caller would never want to put it in a self-referencing sequence.

I'll have to check this out today to see.

	Mel.