Add messages implementation for python #165

elchupanebrej · 2023-07-18T18:08:37Z

🤔 What's changed?

Add python implementation

🏷️ What kind of change is this?

⚡ New feature (non-breaking change which adds new behaviour)

📋 Checklist:

I agree to respect and uphold the Cucumber Community Code of Conduct
I've changed the behaviour of the code
- I have added/updated tests to cover my changes.
Users should know about my change
- I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

This text was originally generated from a template, then edited by hand. You can modify the template here.

elchupanebrej · 2023-07-18T18:11:58Z

This address to #162

mpkorstanje

At a glance this doesn't follow the pattern used by the other language implementations in quite a few ways. Please follow up the directions from #162 around code generation.

I also don't understand the purpose of the samples directory.

elchupanebrej · 2023-07-19T12:50:14Z

@mpkorstanje

For Python exists a tool that allows generating Pydantic models directly from json schema https://github.com/koxudaxi/datamodel-code-generator - So this allows not including an extra layer with templating. If you insist - I'll rewrite this by that approach.
Samples are taken from gherkin repository to validate if serialization/deserialization works well. Adding external data to a python package is always an egg-chicken problem. I don't like to add external files by makefiles or any kind of scripts because they are always platform dependent. If another approach is used in cucumber - please let me know, and I'll adapt this PR

mpkorstanje · 2023-07-19T15:34:16Z

For Python exists a tool that allows generating Pydantic models directly from json schema

You can use Pydantic if you can make it fit into the make clean-all generate-all workflow. Though I suspect your manual edits might pose a problem.

Samples are taken from gherkin repository to validate if serialization/deserialization works well.

Consider narrowing this down to a few representative examples. Currently it is hard to see the forest for the trees.

luke-hill

If you're going to copy lots of the cck it would be better to fetch the data using some form of call rather than C+P as this is currently being rapidly updated

python/pyproject.toml

.github/workflows/test-python.yml

python/RELEASING.md

mpkorstanje · 2024-01-04T12:55:15Z

@elchupanebrej

Samples are used in tests. More complex tests could exist. I insist to include them for now

What purpose do these tests serve? They'll be a hassle to update if/when the schema changes.

luke-hill · 2024-04-04T14:46:02Z

Hi @elchupanebrej - Just checking in to see where you're up to with this. Is this something you're still working on?

elchupanebrej · 2024-09-04T17:13:54Z

Hi @elchupanebrej - Just checking in to see where you're up to with this. Is this something you're still working on?

Hi @luke-hill, sorry for the long response, hadn't time to work on the project. I'll try to create another merge request that will conform to the building process.

elchupanebrej · 2024-09-04T20:59:59Z

The PR was updated with Makefile. Model is stable, so generated code is totally same to version, which was generated at first try

@mpkorstanje I kindly ask you to review the code and take a release part. I didn't get into all deps&relations between release tools.

python/tests/test_model_load.py

mpkorstanje · 2024-09-04T21:26:39Z

Left a few quick remarks, will have to take a deeper look later.

python/Makefile

luke-hill · 2024-09-05T13:22:06Z

python/src/message_samples/minimal/minimal.feature.ndjson

@@ -0,0 +1,12 @@
+{"meta":{"ci":{"buildNumber":"154666429","git":{"remote":"https://github.com/cucumber-ltd/shouty.rb.git","revision":"99684bcacf01d95875834d87903dcb072306c9ad"},"name":"GitHub Actions","url":"https://github.com/cucumber-ltd/shouty.rb/actions/runs/154666429"},"cpu":{"name":"x64"},"implementation":{"name":"fake-cucumber","version":"16.3.0"},"os":{"name":"darwin","version":"22.4.0"},"protocolVersion":"22.0.0","runtime":{"name":"node.js","version":"19.7.0"}}}


I think this is a good process what you've done here. Just commenting for documentation.

I think as/when you have gotten this all working, it would be good to migrate this and others to the CCK proper. WDYT? (Maybe something for 2025?)

migrate this and others to the CCK proper
It must work with CCK now in all possible cases. If it doesn't - let write tests & fix

@elchupanebrej As a test I'm not happy with a "sample test". As said before this create a circular dependency between the code that generates the samples and messages.

Tests for messages can be limited to testing whether the code was generated and serialization works correctly. This is does not test those things specifically while still testing many other - less relevant things.

@luke-hill what exactly do you mean by "migrating this and others to the cck"?

@mpkorstanje sorry for bothering you, it seems I can't catch a point:

Samples of messages in the CCK repository are stored as examples. Every tool that uses messages has to use them (at least serialize when some event is emitted, and deserialize when this message comes to some reporter). So I took the full suite of test data from the CCK repo and checked that the models generated were successfully parsed that messages into the model, and after that deserialized them to totally the same JSON. Could you please describe more precisely what kind of tests would be OK: would be enough if some model(for every kind of message) would be created, serialized and deserialized perfectly to the totally same model?

The CCK uses the messages to generate the output of a canonical cucumber execution. For this is needs the messages. The value the CCK adds isn't that it generates a sample of each messages, but rather that the collection of messages as a whole. So it can for example express relationships between messages.

This dependency also means that it can't be used as test data in messages. That would result in a circular dependency.

Now for messages the exact testing strategy depends on the framework and language used.

For example for Javascript, the object and it's json representation are almost identical so there is little to test at all. And because the code is generated, it doesn't seem nesesary to test every message either.

So you can see we do a round trip test of one moderately complex message and not much more.

https://github.com/cucumber/messages/blob/main/javascript/test/messagesTest.ts

For Java serialization is more complicated. It does not have a concept of undefined. So we got tests to check for that.

https://github.com/cucumber/messages/blob/main/java/src/test/java/io/cucumber/messages/NdjsonSerializationTest.java

Now I don't know enough about Python to tell you exactly what to test. I can't tell you about pitfalls I don't know about. But I imagine if third party code generator is used, a simple round trip should be enough.

To add as well. For the ruby implementation we don't even do something that complex. All we do is "open" the message (Which is an Envelope class), then reclose it again. And check that in doing so we don't change anything. https://github.com/cucumber/messages/blob/main/ruby/spec/cucumber/messages/acceptance_spec.rb

If you're finding that you're going down the rabbit hole of doing lots of testing here, then something is likely going wrong. Messages are the building block that everything else is based off, not the other way around.

Copied ruby approach

mpkorstanje

There seems to have been a misunderstanding.

So just to clarify.

Either:

Source is generated by the Ruby codegen script
Generated source is checked in

Or:

Source is generated by the python build process.
Generated source is not checked in.
Make targets print a message that code code gen is handled by Python.

Which option are you going for now?

.github/workflows/test-python.yml

python/Makefile

python/pyproject.toml

mpkorstanje · 2024-09-08T11:39:41Z

python/src/message_samples/minimal/minimal.feature.ndjson

@@ -0,0 +1,12 @@
+{"meta":{"ci":{"buildNumber":"154666429","git":{"remote":"https://github.com/cucumber-ltd/shouty.rb.git","revision":"99684bcacf01d95875834d87903dcb072306c9ad"},"name":"GitHub Actions","url":"https://github.com/cucumber-ltd/shouty.rb/actions/runs/154666429"},"cpu":{"name":"x64"},"implementation":{"name":"fake-cucumber","version":"16.3.0"},"os":{"name":"darwin","version":"22.4.0"},"protocolVersion":"22.0.0","runtime":{"name":"node.js","version":"19.7.0"}}}


@elchupanebrej As a test I'm not happy with a "sample test". As said before this create a circular dependency between the code that generates the samples and messages.

Tests for messages can be limited to testing whether the code was generated and serialization works correctly. This is does not test those things specifically while still testing many other - less relevant things.

@luke-hill what exactly do you mean by "migrating this and others to the cck"?

python/src/message_samples/minimal/minimal.feature.ts

mpkorstanje · 2024-09-08T11:40:54Z

python/src/messages.py

@@ -0,0 +1,3 @@
+from _messages import *
+
+ExpressionType = Type1


I don't understand what this file does. Can you explain?

We have two entities in the original model named Type (design bug from my perspective). This module is a simple adapter, so the end user will import Type and ExpressionType but not Type and Type1. In the serialized model they both are named Type as it was in the original model

Would it be possible to fix that in the code generator instead?

And if it is not possible, an explanatory comment would be useful.

python/src/_messages.py

python/src/message_samples/__init__.py

youtux · 2024-09-15T16:01:09Z

python/pyproject.toml

+]
+dependencies = [
+  "importlib_resources",
+  "pydantic>=2.0.3"


Is it really necessary to use and add pydantic as a dependency ?
Many people are still on pydantic v1, and this would require pytest-bdd users to upgrade to pydantic v2 since pytest-bdd will soon depend on gherkin

Aren’t stdlib dataclasses enough?

importlib_resources is also, from what I can see, only used for tests which I'm not sure is needed either

@youtux Yes, this is technically possible, but such realization will be dependent on some library like https://github.com/lidatong/dataclasses-json (the best option for now), which are not as good supported as pydantic

From another perspective - testing utilities are selected at the start of a project, so if the messages package will be used somewhere - it most probably would be dependent on the new version of Pydantic

but there are many projects using pytest-bdd for years, and this would be an issue.
We can do without pydantic in a very simple way. We can use data classes, then when we need to serialise to json we call asdict(model). If we need custom encoders (e.g. for date times) we can implement a simple JsONEncoder and pass that to json.dumps(asdict(model), encoder=…).

Or also just implement custom serialiser for each object

in this case, we have to implement dict_factory for dataclass.asdict, which will have to take in count Enums, or there would be an issue with serialization to JSON. And deserialisation to the dataclass also will be an issue (Enums again)
And pydantic covers both of this issues

I really think we should not bring in a big dependency like pydantic here, especially since it has made a big API change in v2, and I can see it make it difficult for users to adopt this library if it conflicts with their pydantic v1 requirement.

What's the use of pydantic here? I don't see it being used for serialisation / deserialisation here.
What's the API of this library going to look like?

Messages library is hardly used for serialization/deserialization, for example:

Test runner must produce messages in the ndjson format, so it uses model of "messages" lib to represent outcomes, messages lib serializes and validates against Json schema (non-directly).

Test reporter consumes ndjson stream of messages and uses "messages" library to deserialize inputs and validate them.

So "messages" lib is a bridge between test runner and test reporter (potentially from different languages ecosystems)

ok, but how is the API of this lib supposed to look like?

from cucumber_messages import ??? ???

@youtux , please check python/tests/test_model_load.py test in this PR (I'll rework tests later).

For example reporting in the pytest-bdd-ng uses this particular model:
https://github.com/elchupanebrej/pytest-bdd-ng/blob/default/src/pytest_bdd/message_plugin.py

Exrta dependencies were declined

elchupanebrej · 2024-09-17T05:41:08Z

Thanks for great review, return later this week and will update all things accordingly 😀

python/.pre-commit-config.yaml

python/src/cucumber_messages/json_converter.py

elchupanebrej · 2024-12-13T18:23:36Z

This would use lidatong/dataclasses-json#442 in future

elchupanebrej · 2024-12-19T00:26:10Z

@mpkorstanje @luke-hill @jsa34 @youtux
Please make a new review for this PR:

Model doesn't use Pydantic anymore (dataclasses are used)
Model generation leverage on ruby templates (so no more Makefile workarounds)
Tests are provided in the same manner as at other language implementations

luke-hill

I've reviewed 2/3rds of this PR so far and only got a couple of questions. So I'll pass that in for now. The other items are a bit more complex and I'll review at a later date (Might be after xmas now).

luke-hill · 2024-12-19T09:52:37Z

.github/workflows/test-codegen.yml

@@ -31,6 +31,11 @@ jobs:
        with:
          ruby-version: '3.1'

+      - name: Set up Python


Do we need python now for codegen?

No, I'll update

luke-hill · 2024-12-19T09:53:43Z

.pre-commit-config.yaml

@@ -0,0 +1,50 @@
+# See https://pre-commit.com for more information


Should this file be gitignored. Or should a common style be enforced. It seems as though some styles have been a source of contention throughout this/other PRs?

I could gitignore it for a while, but it marks that it works only in the python directory

luke-hill · 2024-12-19T10:02:15Z

codegen/templates/python.py.erb

@@ -0,0 +1,68 @@
+# This code was generated using the code generator from cucumber-messages.


Whilst it's not mandatory usually we split the two templates up into an enum template and a non-enum (Standard class), template.

Usually this is because the enums generate just some simple readers for each constant whereas the class usually has some primitive behaviour (like serialization / deserialization).

An example of the complexity difference in ruby would be these two

ENUM: Just has constant definitions https://github.com/cucumber/messages/blob/main/ruby/lib/cucumber/messages/attachment_content_encoding.rb

Class: Has some basic readers/serialization logic (Note the attr_readers and the .from_h method https://github.com/cucumber/messages/blob/main/ruby/lib/cucumber/messages/attachment.rb

The template is really simple, and all serialization/deserialization is done externally. Actually https://pypi.org/project/marshmallow-dataclass/ could be used instead of proposed serialization/deserialization approach

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Add python implemeatation to official messages library elchupanebrej/pytest-bdd-ng#104

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[python] Add messages implementation for python

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		@@ -0,0 +1,12 @@
		{"meta":{"ci":{"buildNumber":"154666429","git":{"remote":"https://github.com/cucumber-ltd/shouty.rb.git","revision":"99684bcacf01d95875834d87903dcb072306c9ad"},"name":"GitHub Actions","url":"https://github.com/cucumber-ltd/shouty.rb/actions/runs/154666429"},"cpu":{"name":"x64"},"implementation":{"name":"fake-cucumber","version":"16.3.0"},"os":{"name":"darwin","version":"22.4.0"},"protocolVersion":"22.0.0","runtime":{"name":"node.js","version":"19.7.0"}}}

		@@ -0,0 +1,3 @@
		from _messages import *

		ExpressionType = Type1

		@@ -0,0 +1,50 @@
		# See https://pre-commit.com for more information

		@@ -0,0 +1,68 @@
		# This code was generated using the code generator from cucumber-messages.

Add messages implementation for python #165

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Add messages implementation for python #165

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elchupanebrej commented Jul 18, 2023

🤔 What's changed?

🏷️ What kind of change is this?

📋 Checklist:

elchupanebrej commented Jul 18, 2023

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