f-strings are usually preferred to concatenation: print(f"{result.id} => {result.data}")

suggestion: Python lets you break up large numbers, so you could do 100_000 for readability (and consider this for other large numbers in this file)

It looks like result.data is a method and not a property, so I think you need to call it: result.data()

you can also do Constant.of("Toronto"), to match Field.of. I'm not sure which is preferred

We also have an async version of everything.

Often, we re-write the samples for both sync and async, and show both options in the language selection pickers. I'm not sure how you want to handle that here.

Maybe a couple samples for pipeline_initialization_async and basic_read_async is enough to show it exists, since the API is almost identical. Or maybe samples for async aren't needed for preview

Maybe you should include the import in the sample? from google.cloud.firestore_v1.pipeline_expressions import And. I guess this feedback would apply to Field and Constant too though...

Our usual policy was that samples should all include relevant imports. Most of these pipeline tests don't really need imports. But when we start adding Ands and Ors and Nots, I could see users getting confused, since they look so close to built-in methods

We do have a Vector type, maybe we should recommend users use that instead of a raw list? Vector([0.0, 1.0, 2.0, 3.0, 4.0, 5.0])

We support both though, so if you think this is easier/cleaner, this works too

It would be great if we could have a test file that exercises these functions. Even just running them without verifying outputs would be helpful to make sure no exceptions are thrown, but reading back results would be ideal

It looks like the other samples in this repo aren't tested though, so maybe that would be too much to set up

We usually use the black code formatter for our Python code. If you haven't used it, it might be good to run it over this file to see if it has any changes

Nothing really stands out to me as badly formatted, and I don't think using that formatting should be a requirement for samples. But it might be worth checking

If you want to get rid of all the \, IIRC think you could do something like this:

results = (
    client.pipeline()
    .collection("books")
    .aggregate(
        Field.of("rating").average().as_("avg_rating"),
        groups=[Field.of("genre")]
    ).execute()
)

(But test it first)