tobgu/pyrsistent

`setdefault`, or some superior functionality as part of `transform()`

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#95 opened on Feb 3, 2017

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enhancementhelp wanted

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Description

Consider the following code:

class ApplicationState(PClass):
    shared_resources = pset_field(Injectable)
    # ...

class ExtractedState(PClass):
    applications = pmap_field(str, ApplicationState)

def extract(tfstate):
    result = {}

    for mod in tfstate['modules']:
        for injectable in _extract_resources_from_module(mod):
            app_state = result.setdefault(injectable.app,
                                          {"shared_resources": set(),
                                           "service_resources": {}})
            app_state["shared_resources"].add(injectable)

   return ExtractedState.create(freeze({"applications": result}))

Constructing the pyrsistent objects is quite annoying, which is why I'm doing it with mutable objects, due to lack of setdefault or "create a default object in transform()". Ideally I'd do:

extracted_state = ExtractedState()
extracted_state = extracted_state.transform(
    ["applications", "newapp", "shared_resources"], lambda ps: ps.add(obj))

but since newapp doesn't exist it blows up...

Contributor guide

Research direction
Investigate how to add a setdefault like functionality to the transform method, or implement a separate setdefault method on PMap. Look at existing transform implementation to understand how to create default objects when keys are missing.
Tech stack
python
Domain
backenddeveloper experience
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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Active
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Clear
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PythonGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70