another thought here: it’s possible that it would be both more ergonomic and a bit more performant if we deprecated

interpreter_constraints

on targets as defining an actual list, and replaced it with a reference to a name/slug defined globally:

$ cat BUILD
python_library(
  interpreters='default',
)

python_library(
  interpreters='unusual',
)
$ cat pants.toml
..
[python-setup]
interpreters = """{
    'default': '[">=3.7,<3.10"]',
    'unusual': '["==2.7.*", "==3.5.*"]',
}"""

…because then you’d have a closed universe of interpreters