I am facing the following error while I am trying to run pants in a new repo. Any idea?

pants.option.errors.ParseError: Error computing value for --requirement-constraints in scope 'python' (may also be from PANTS_* environment variables).
Caused by:
File value `constraints.txt` for option `requirement_constraints` in `scope 'python'` does not exist.

Hi, The message indicates that you don’t have the

constraints.txt

file. You’ll have to create it yourself. I’m assuming you’re on 2.9.0, in which case this section is relevant for you: https://www.pantsbuild.org/docs/python-third-party-dependencies#lockfiles notably the phrase “To use a lockfile, first generate a

constraints.txt

file, such as by using one of these techniques” Let us know if this makes sense 🙂

Hi! Andreas I'm not sure that's it - if the file didn't exist, the error would be different saying that the file does not exist. This is saying the option is not legal @wide-zoo-86070 how are you setting this option? e.g. pants.toml?

Oh! Riiight, that error message is having me confused. May I suggest rephrasing, so what is important is presented sooner. What the value was is secondary for invalid options.. ;)

I definitely did not generate constraints.txt. I will try to do it and revert back. Btw, where is the benefit of using this constraints.txt.

It is to pin your dependencies, so you know exactly which version is being used.

Oh dang you're right. Good eye / apologies!

I am wondering how pants handle multiple requirements.txt. Suppose below is the structure of the repo

-project_A
   -requirements.txt
-project_B
   -requirements.txt
-env.yaml
-requirements.txt

The env.yaml will have something like below to use with conda

- pip:
  - -r requirements.txt
  - -r project_A/requirements.txt
  - -r project_B/requirements.txt

How pants handle such cases? e.g. do i need to generate a single constraints.txt which includes all requirements.txt?

The story got a lot better in Pants 2.10, which is close to a stable release 🙂 https://pantsbuild.slack.com/archives/C046T6T9U/p1647295890676559

@wide-zoo-86070 you can have multiple lockfiles in 2.10, as Eric mentions, but the key point is that you don't have to. You can have a single global requirements.txt (and accompanying lockfile), and Pants will take just the necessary subset as needed.