When assigning, how to generate a different missing structure based on path type?

[foucdeg]

Starting from an empty dict, I might make assignments like this:

glom.assign({}, "a.0.b", "value", missing=?)

The result I expect is the following:

{ 'a': [ { 'b': 'value' } ] }

although I understand that it could also be interpreted as

{ 'a': { '0': { 'b': 'value' } } }

This means that I want the missing function to create a list for the missing structure "a", and a dict for the missing structure "a.0".
Unfortunately, missing isn't called with any arguments that would allow me to return a list or a dict depending on whether the next path part is an int or a string.

Is there some other way to do what I want?

[kurtbrose]

that's a great suggestion, providing arguments to missing

[Kwill3]

Here to bump this issue and check if any progress has been made on this? Otherwise is there another way we can assign between lists and dicts on current version?

[mahmoud]

@Kwill3 we haven't really done anything with this. I think everyone's open to the idea, though.

I guess the next step in the conversation is to ask what arguments would be useful? We could pass the current path, the current glom scope (possibly too technical for day-to-day use), just the name of the current field, etc.?

A really cool thing would be to create one's own spec type (forked from Assign) and experiment, if you'd like to help advance the feature. Docs on spec type creation are here: https://glom.readthedocs.io/en/latest/custom_spec_types.html

[ajslater]

Here's a suggestion:

Usage

from glom import glom, Assign, MATCH
result = glom(target_dict, Assign("a.b.0.c", value, missing=MATCH))

Code

mutation.py:

MATCH = "match"

https://github.com/mahmoud/glom/blob/master/glom/mutation.py#L173

        except PathAccessError as pae:
            if not self.missing:
                raise

            remaining_path = self._orig_path[pae.part_idx + 1:]
            # NEW CODE STARTS HERE
            if self.missing == MISSING_MATCH:
                # Naive idea about how to figure out this path level's type. The maintainers will have
                # more context about wether this is adequate.
                this_path_level = self._orig_path[pae.part_idx]
                # AFAIK glom only supports two types with path notation.
                # Alternatively we could look at the parent target or parent dest's type
                missing = list if this_path_level.isnumeric() else dict
            else:
                missing = self.missing
            val = scope[glom](missing(), Assign(remaining_path, val, missing=self.missing), scope)