Hey folks; when I run

pants package src/lambdas/whatever

I get a little bit of metadata:

14:37:05.54 [INFO] Wrote dist/src.lambdas.whatever/whatever.zip
    Runtime: python3.12
    Architecture: x86_64
    Handler: lambda_function.handler

Is there any way to have that metadata output to a file instead? (My bash is weaker than I thought it was, I don’t seem to be able to pipe it to a file from stdout or stderr either!) I’d like to be able to configure my terraform to set up my lambda with the runtime, arch, and handler as configured in pants, so I don’t have duplicate info — if I can get this into a JSON/similar file, I can configure Terraform to read it and use those values 💪

Do you have this information in the target? If so, you could use

pants peek

Oh nice! Thanks! I can get the

handler

, and

architecture

, but the Python version is set at the monorepo level, so I presume it’s not pulled up to being able to peek at the target?

[python]
interpreter_constraints = ["==3.12.*"]

If it’s useful, here’s the

jq

command for extracting the handler & architecture:

pants peek src/lambdas/whatever | jq '.[] | select(.target_type == "python_aws_lambda_function") | {handler: (.handler | sub("\\.py:"; ":")), architecture}'

I’ll keep hunting for ways to pull the runtime version out — I don’t really want to have to specify it in the

BUILD

for every lambda (as the whole point here is to minimize duplicate config)

You can set this in your root BUILD:

__defaults__(all=dict(interpreter_constrains=["==3.12.*"]))

Then it should show up in peek output

Thanks @square-psychiatrist-19087 — does setting

interpreter_constraints

in the

pants.toml

not do the same? (I don’t have a root

BUILD

at the moment, but I could make one for defaults — it just seems odd to not have the interpreter constraints in the pants.toml not be used here?)

It does get used, but pants.toml is a separate mechanism for defaults. Basically in the pants backend there is code something like this:

if target.interpreter_constraints is not None: 
    return target.interpreter_constraints
else:
    return config.interpreter_constraints

So if the target doesn't have interpreter constrains it will look it up in pants.toml. However,

pants peek

can't do that and only looks at target values. This

__defaults__

trick sets the value on the target, so it becomes visible to

pants peek

I can’t seem to get any info on what Python version is being used with

pants peek

, regardless of where I define my contraints: • as a default in my root

BUILD

(as you describe above) • with

python_sources(interpreter_constraints=["==3.12.*"])

in my lambda’s

BUILD

• in the pants.toml in the

[python]

section as an

interpreter_constraints

parameter • in the lambda’s

pyproject.toml

(as a poetry dependency, used with a

poetry_requirements

in the lambda’s

BUILD

) I can get most of what’s output with

pants package src/lambdas::

with

jq

and

pants peek

, but not everything:

$ pants package src/lambdas::
09:50:12.32 [INFO] Wrote dist/src.lambdas.whatever/whatever.zip
    Runtime: python3.12
    Architecture: x86_64
    Handler: lambda_function.handler

$ pants peek src/lambdas:: | jq '.[] | select(.target_type == "python_aws_lambda_function") | {path: (.address | sub(":.*$"; "")), handler: (.handler | sub("\\.py:"; ".")), architecture}'
{
  "address": "src/lambdas/whatever",
  "handler": "lambda_function.handler",
  "architecture": "x86_64"
}

(I also have to do extra bash to split the records & convert

address

into the output path

dist/src.lambdas.whatever/whatever.json

for each of the results

pants peek

returns)

Do you set

runtime

for your lambda? https://www.pantsbuild.org/stable/reference/targets/python_aws_lambda_function

Ahh super, thankyou! That does work! 🥳 The only problem is, I’m now setting my python runtime in two places; once for the local python interpreter (in my

pyproject.toml

, which is calculated by inference by

pants package

and output to the terminal), and once in my

BUILD

for in

python_aws_lambda_function(runtime="python3.12")

. Any ideas on how to get

peek

to output the inferred python runtime?

How do you set your python dependencies? via

dependencies

or

handler

?

This might work, but I’m going to have multiple pythons in my monorepo 😔 Thank you so much for your help here, you’ve offered so many tips for some stranger who has a rather specific request 😅

No, that's actually a natural request, pants is mostly a metadata layer on top of your existing code, so it's whole purpose is to provide ways to inspect metadata I think there was a feature request to read external files directly from BUILD, but I don't think it was implemented

So such luck; possibly because I’m using

poetry

to manage my python version? I’ve put all the relevant bits in this gist (note that I’ve switched to python 3.13 since we started this conversation). I’ve got to duck out for the rest of the day — so I won’t be able to reply for a while, but thanks for your help & thoughts!

Separately from this workaround, it seems like a reasonable feature to have, and it would not be difficult to add.

That sounds superb! Let me know if I can be of any help!