bazel, python rules, created files how to get them

Question

How can I access files that my python is creating?
so inside a python i got something like:

from pathlib import Path
p = Path('my_file.txt')
p.write_text('testing')
print("Testing done")

then when i do bazel run my_file i can see in terminal text that all went well and info from print, but when i am trying to find my_file.txt there is nothing. So what do i need to do with my rules to be able to access that file after bazel run is done?

Answer 1

It might help if you can give some more details:

1. How is that python code being run? Is it being run as an action?
2. What is the my_file target?
3. You mention that you have some rules. Are these Starlark rules that you wrote?

But to answer directly: When a binary is run with bazel run, it's executed in a "runfiles tree" that contains symlinks of all the dependencies of the binary. So your file will be put in the binary's runfiles directory.

my_program.py:

import os
from pathlib import Path

print("current working directory: " + os.getcwd())

p = Path('my_file.txt')
p.write_text('testing')
print("Testing done")

BUILD:

py_binary(
  name = "my_program",
  srcs = ["my_program.py"],
)

$ bazel run my_program
INFO: Analyzed target //:my_program (18 packages loaded, 90 targets configured).
INFO: Found 1 target...
Target //:my_program up-to-date:
  bazel-bin/my_program
INFO: Elapsed time: 0.226s, Critical Path: 0.01s
INFO: 5 processes: 5 internal.
INFO: Build completed successfully, 5 total actions
INFO: Build completed successfully, 5 total actions
current working directory: /home/ahumesky/.cache/bazel/_bazel_ahumesky/5123c9882cdbb6c5e34f583431173549/execroot/__main__/bazel-out/k8-fastbuild/bin/my_program.runfiles/__main__
Testing done

$ ls /home/ahumesky/.cache/bazel/_bazel_ahumesky/5123c9882cdbb6c5e34f583431173549/execroot/__main__/bazel-out/k8-fastbuild/bin/my_program.runfiles/__main__
external  my_file.txt  my_program  my_program.py

$ cat /home/ahumesky/.cache/bazel/_bazel_ahumesky/5123c9882cdbb6c5e34f583431173549/execroot/__main__/bazel-out/k8-fastbuild/bin/my_program.runfiles/__main__/my_file.txt 
testing

If possible, it might be better if you pass the output file path to the program as an argument, so that the file is at some known location:

import sys
from pathlib import Path

p = Path(sys.argv[1])
p.write_text('testing')
print("Testing done")

$ bazel run my_program -- /tmp/output.txt
INFO: Analyzed target //:my_program (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //:my_program up-to-date:
  bazel-bin/my_program
INFO: Elapsed time: 0.040s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Build completed successfully, 1 total action
Testing done

$ cat /tmp/output.txt
testing

Alternatively, if you run the program directly, then the file will be in the current working directory:

$ bazel build my_program
INFO: Analyzed target //:my_program (18 packages loaded, 90 targets configured).
INFO: Found 1 target...
Target //:my_program up-to-date:
  bazel-bin/my_program
INFO: Elapsed time: 0.219s, Critical Path: 0.01s
INFO: 5 processes: 5 internal.
INFO: Build completed successfully, 5 total actions

$ bazel-bin/my_program
current working directory: /home/ahumesky/test
Testing done

$ cat my_file.txt
testing

Answer 2

write_text() returns the number of characters written to the text file, maybe you can check for that. Or, try print(p.read_text())

Answer 3

Look at that script: you can use the BUILD_WORKING_DIRECTORY env variable to create a path to the file in a working directory