CONTRIBUTING.rst

Contributing

Issues and Pull Requests are very welcome!

Here are some notes about the project that may help make pull requests easier to merge.

The environment

Everything that is needed is available in a virtualenv in the current terminal session by doing:

> source dev activate

Even if this has been done before, doing it again will install new dependencies if the version of Photons has changed.

The tests

For the core tests run from any folder:

> ./modules/test.sh

For the interactor tests run from any folder:

> ./apps/interactor/test.sh

Tests are grouped by their module inside the tests folder. Note that we name each folder as "<module>_tests" so that import statements for that module don't get clobbered by these test files.

Code style

We use the black project (https://black.readthedocs.io/en/stable/) to format the python code in this repository.

All the developer needs to know is that either their editor is run in the same session as a source dev activate or that they run:

$ ./format

Import sorting

Photons uses default settings on isort to sort imports

Using import as

I tend to import things directly, but I do tend to shortcut photons_app.helpers

from photons_app import helpers as hp

Linting

I use pylama as my code linter and can be run from:

$ ./lint

Commits

Please follow Linus' guide for good commit messages.

And also have in the title the module or app you are working on:

interactor: Fix some memory leaks

It's possible for python to hold onto frame objects via exceptions so I need to be more careful about holding onto those

Here the short description starts with a tag of sorts in square brackets and a short sentence of what. Followed by a paragraph with how and why.

Comments

Comments in code should explain why something is done more than what is being done.

Exception is when code is very complicated and it may be difficult to understand what is happening.

Variable names

It's incredibly important to try your best to name things consistently. No types means when changes are made, this makes it a lot easy/possible to ensure that you find all instances of something that must be changed.

Commented out code

Please do not commit commented out code. Delete it. It's in git history.

async context managers

In Python, a context manager is a cleanup mechanism that uses the with syntax.

For example, instead of saying:

wrapper = MyWrapper()

wrapper.start()
try:
    do_something()
finally:
    wrapper.finish()

You would write:

with MyWrapper() as wrapper:
    do_something()

An async context manager is the same, but uses the async/await syntax as well:

async with MyWrapper() as wrapper:
    do_something()

Photons can create these in two ways.

The first way is using the standard library asynccontextmanager decorator. Photons makes this available via photons_app.helpers to make it easier to sync with public photons until the minimum version of Python supported by it is Python3.7 as Python3.6 does not include that function in the standard library and public photons must polyfill it.

from photons_app import helpers as hp


@hp.asynccontextmanager
async def wrap():
    try:
        await something_fun()
        yield
    finally:
        await some_cleanup()

The other way is via manually defining one in a class. The protocol in Python for a context manager is __enter__()/__exit__(exc_typ, exc, tb) for synchronous context managers and __aenter__()/__aexit__(exc_typ, exc, tb) for asynchronous context managers.

In Python a context manager is the same as:

await wrapper.__aenter__()
try:
    do_something()
finally:
    await wrapper.__aexit__(...)

But for cleanup purposes it is useful to instead have:

try:
    await wrapper.__aenter__()
    do_something()
finally:
    await wrapper.__aexit__(...)

To make this possible, Photons supplies hp.AsyncCMMixin and you implement start()/finish(exc_typ=None, exc=None, tb=None):

from photons_app import helpers as hp


class Thing(hp.AsyncCMMixin):
    async def start(self):
        ...

    async def finish(self, exc_typ=None, exc=None, tb=None):
        ...

This means all async context managers in Photons will run finish even if an exception is raised in start, and have start and finish if you are not using the with syntax.

Visual studio code

See .vscode/README.rst.