tree b81c5eaff2ebbbb7d49f927d4aa6237dccdf788a
parent b80c74fb6a95992e0af4b698ac9c9f822e050788
author Yilei Yang <yileiyang@google.com> 1564692201 -0700
committer Copybara-Service <copybara-worker@google.com> 1564692219 -0700

Stop modifying `logging.root.handlers` when importing `absl.logging`.

Users who (indirectly) import `absl.logging` and don't use `absl.app.run()` will no longer have this side-effect, and `absl.logging` behaves like a good citizen.

For `absl.app.run()` users: this has behavior changes for log calls between "absl.logging is first imported" and "app.run()" is called, a.k.a. "logs at import time".

Logs at import time now have the format like:
    WARNING:root:import time logs coming from standard `logging`
or:
    WARNING:absl:import time logs coming from `absl.logging`
instead of:
    W0719 14:52:00.084659    8465 other_lib.py:4] import time logs coming from either standard `logging` or `absl.logging`
And it no longer warns "WARNING: Logging before flag parsing goes to stderr."

If you need the previous behavior for logs at import time, you can call `absl.logging.use_absl_handler()` before importing any other module.

PiperOrigin-RevId: 261188705
Change-Id: I09331d22c95cf52ce8485a6372664b3c1ddd3445