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Debug log, logging improvements (#3159)

Browse Source 
* simplify logging

* remove comment

* progress on debug.log

* add debug-level logger for file log

* simplify

* case insensitivity; 3rd party logging improvements

* simplify

* fix

* tests

* lint

* nits

* nit

* Update tests/test_utils_tee.py

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* cleanup / comments

* fix

* oops

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>
This commit is contained in:
Dan Saunders
2025-09-17 13:27:03 -04:00
committed by GitHub
parent e5c427f6de
commit 4065bc14c6
20 changed files with 454 additions and 69 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
.gitignore vendored
View File

@@ -190,3 +190,6 @@ out/
# vim
*.swp
# scm auto-versioning
src/axolotl/_version.py

2
.pre-commit-config.yaml
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@@ -14,7 +14,7 @@ repos:
rev: v0.12.12
hooks:
- id: ruff
args: [--fix, --select, I]
args: [--fix]
- id: ruff-format
- repo: https://github.com/pre-commit/mirrors-mypy
rev: v1.17.1

6
examples/colab-notebooks/colab-axolotl-example.ipynb
View File

@@ -251,10 +251,10 @@
},
"outputs": [],
"source": [
"from axolotl.utils import patch_optimized_env\n",
"from axolotl.utils import set_pytorch_cuda_alloc_conf\n",
"\n",
"# speedup downloads from HF 🤗 and set \"PYTORCH_CUDA_ALLOC_CONF\" env to save memory\n",
"patch_optimized_env()"
"# Set \"PYTORCH_CUDA_ALLOC_CONF\" env to save memory\n",
"set_pytorch_cuda_alloc_conf()"
]
},
{

2
pyproject.toml
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@@ -32,7 +32,7 @@ line-length = 88
target-version = "py310"
[tool.ruff.lint]
select = ["E", "F", "W", "C90", "B"]
select = ["E", "F", "W", "C90", "B", "I"]
ignore = [
"E203", # Whitespace before ':'
"E501", # Line too long

4
src/axolotl/cli/__init__.py
View File

@@ -4,5 +4,7 @@ import os
from axolotl.logging_config import configure_logging
os.environ["HF_HUB_ENABLE_HF_TRANSFER"] = "1"
os.environ.setdefault("TOKENIZERS_PARALLELISM", "false")
os.environ.setdefault("HF_HUB_ENABLE_HF_TRANSFER", "1")
configure_logging()

9
src/axolotl/cli/config.py
View File

@@ -23,7 +23,8 @@ from axolotl.utils.config import (
from axolotl.utils.dict import DictDefault
from axolotl.utils.logging import get_logger
from axolotl.utils.mlflow_ import setup_mlflow_env_vars
from axolotl.utils.trainer import prepare_opinionated_env, prepare_optim_env
from axolotl.utils.tee import prepare_debug_log
from axolotl.utils.trainer import prepare_optim_env
from axolotl.utils.wandb_ import setup_wandb_env_vars
LOG = get_logger(__name__)
@@ -227,8 +228,11 @@ def load_cfg(
},
)
# NOTE(djsaunde): We start outputting to output_dir/debug.log at this point since we
# have to wait for cfg.output to be resolved. We could call this earlier if we write
# to a temporary file, and then move it later.
prepare_debug_log(cfg)
prepare_optim_env(cfg)
prepare_opinionated_env(cfg)
normalize_config(cfg)
normalize_cfg_datasets(cfg)
setup_wandb_env_vars(cfg)
@@ -241,7 +245,6 @@ def load_cfg(
for k, v in cfg.items()
if v is not None
}
LOG.info(
"config:\n%s",
json.dumps(cfg_to_log, indent=2, default=str, sort_keys=True),

2
src/axolotl/cli/inference.py
View File

@@ -17,8 +17,6 @@ from axolotl.cli.utils import load_model_and_tokenizer
from axolotl.cli.utils.diffusion import (
diffusion_inference,
launch_diffusion_gradio_ui,
render_html,
run_diffusion,
)
from axolotl.integrations.base import PluginManager
from axolotl.utils.chat_templates import get_chat_template_from_config

4
src/axolotl/cli/main.py
View File

@@ -26,7 +26,7 @@ from axolotl.cli.utils import (
launch_training,
)
from axolotl.integrations.lm_eval.cli import lm_eval
from axolotl.utils import patch_optimized_env
from axolotl.utils import set_pytorch_cuda_alloc_conf
from axolotl.utils.logging import get_logger
from axolotl.utils.schemas.config import AxolotlInputConfig
@@ -44,7 +44,7 @@ def cli():
"""Axolotl CLI - Train and fine-tune large language models"""
print_axolotl_text_art()
load_dotenv()
patch_optimized_env()
set_pytorch_cuda_alloc_conf()
@cli.command()

1
src/axolotl/cli/train.py
View File

@@ -60,7 +60,6 @@ def do_cli(config: Union[Path, str] = Path("examples/"), **kwargs):
config: Path to `axolotl` config YAML file.
kwargs: Additional keyword arguments to override config file values.
"""
parsed_cfg = load_cfg(config, **kwargs)
parser = HfArgumentParser(TrainerCliArgs)
parsed_cli_args, _ = parser.parse_args_into_dataclasses(

1
src/axolotl/cli/utils/diffusion.py
View File

@@ -3,7 +3,6 @@
from __future__ import annotations
import gradio as gr
import torch
from colorama import Fore, Style
from axolotl.integrations.diffusion import generate, resolve_mask_token_id

75
src/axolotl/logging_config.py
View File

@@ -1,10 +1,7 @@
"""
Common logging module for axolotl
"""
"""Common logging module for axolotl."""
import logging
import os
import sys
from logging import Formatter, Logger, LogRecord
from logging.config import dictConfig
from typing import Any, Dict
@@ -17,9 +14,9 @@ DEFAULT_LOG_LEVEL = "WARNING"
class AxolotlOrWarnErrorFilter(logging.Filter):
"""
Allows ANY WARNING or higher (unless overridden by LOG_LEVEL)
Allows axolotl.* at INFO or higher (unless overridden by AXOLOTL_LOG_LEVEL)
Drops all other records (i.e. non-axolotl.INFO, DEBUG, etc. by default)
Allows ANY WARNING or higher (unless overridden by LOG_LEVEL). Allows axolotl.* at
INFO or higher (unless overridden by AXOLOTL_LOG_LEVEL). Drops all other records
(i.e. non-axolotl.INFO, DEBUG, etc. by default).
"""
def __init__(self, **kwargs):
@@ -52,13 +49,12 @@ class AxolotlOrWarnErrorFilter(logging.Filter):
class AxolotlLogger(Logger):
"""A Logger that automatically rejects non-axolotl INFOs."""
"""Logger that applies filtering to non-axolotl loggers."""
def __init__(self, name: str, level: int = logging.NOTSET):
super().__init__(name, level)
# set global filter on the logger itself
self.addFilter(AxolotlOrWarnErrorFilter())
if not name.startswith("axolotl"):
self.addFilter(AxolotlOrWarnErrorFilter())
class ColorfulFormatter(Formatter):
@@ -74,6 +70,7 @@ class ColorfulFormatter(Formatter):
def format(self, record):
record.rank = int(os.getenv("LOCAL_RANK", "0"))
record.rank_fmt = f" [RANK:{record.rank}]" if record.rank != 0 else ""
log_message = super().format(record)
return self.COLORS.get(record.levelname, "") + log_message + Fore.RESET
@@ -87,32 +84,54 @@ DEFAULT_LOGGING_CONFIG: Dict[str, Any] = {
},
"colorful": {
"()": ColorfulFormatter,
"format": "[%(asctime)s] [%(levelname)s] [%(name)s.%(funcName)s:%(lineno)d] [PID:%(process)d] [RANK:%(rank)d] %(message)s",
"format": "[%(asctime)s] [%(levelname)s] [%(name)s.%(funcName)s:%(lineno)d] [PID:%(process)d]%(rank_fmt)s %(message)s",
},
"concise": {
"format": "[%(asctime)s] [%(levelname)s] [%(name)s] %(message)s",
},
"concise_color": {
"()": ColorfulFormatter,
"format": "[%(asctime)s] [%(levelname)s] [%(name)s]%(rank_fmt)s %(message)s",
},
},
"filters": {
"ax_or_warn": {
"()": "axolotl.logging_config.AxolotlOrWarnErrorFilter",
},
},
"filters": {},
"handlers": {
"console": {
"class": "logging.StreamHandler",
"formatter": "simple",
"filters": [],
"stream": sys.stdout,
"formatter": "concise",
"filters": ["ax_or_warn"],
"stream": "ext://sys.stdout",
},
"color_console": {
"class": "logging.StreamHandler",
"formatter": "colorful",
"filters": [],
"stream": sys.stdout,
"formatter": "concise_color",
"filters": ["ax_or_warn"],
"stream": "ext://sys.stdout",
},
"ax_file_only": {
"class": "logging.StreamHandler",
"level": "DEBUG",
"formatter": "simple",
"stream": "ext://axolotl.utils.tee.file_only_stream",
},
"root_file_only": {
"class": "logging.StreamHandler",
"level": "DEBUG",
"formatter": "simple",
"stream": "ext://axolotl.utils.tee.file_only_stream",
},
},
# log level will be superseded by the AxolotlLogger
"root": {
"handlers": ["console"],
"level": os.getenv("LOG_LEVEL", DEFAULT_LOG_LEVEL),
"handlers": ["console", "root_file_only"],
"level": os.getenv("LOG_LEVEL", DEFAULT_LOG_LEVEL).upper(),
},
"loggers": {
"axolotl": {
"handlers": ["color_console"],
"handlers": ["color_console", "ax_file_only"],
"level": os.getenv("AXOLOTL_LOG_LEVEL", DEFAULT_AXOLOTL_LOG_LEVEL).upper(),
"propagate": False,
},
@@ -123,9 +142,15 @@ DEFAULT_LOGGING_CONFIG: Dict[str, Any] = {
def configure_logging():
"""Configure with default logging"""
init() # Initialize colorama
dictConfig(DEFAULT_LOGGING_CONFIG)
logging.setLoggerClass(AxolotlLogger)
# set default `ACCELERATE_LOG_LEVEL` to `LOG_LEVEL` if available and not set
# Route Python warnings through logging so they reach file handlers
logging.captureWarnings(True)
# Set default `ACCELERATE_LOG_LEVEL` to `LOG_LEVEL` if available and not set
if "ACCELERATE_LOG_LEVEL" not in os.environ:
os.environ["ACCELERATE_LOG_LEVEL"] = os.getenv("LOG_LEVEL", DEFAULT_LOG_LEVEL)
os.environ["ACCELERATE_LOG_LEVEL"] = os.getenv(
"LOG_LEVEL", DEFAULT_LOG_LEVEL
).upper()

6
src/axolotl/monkeypatch/transformers/trainer_loss_calc.py
View File

@@ -41,7 +41,7 @@ def patch_evaluation_loop():
"""Patch the evaluation_loop method."""
# Check if already patched
if hasattr(Trainer, "_original_evaluation_loop"):
LOG.info("Trainer.evaluation_loop already patched")
LOG.debug("Trainer.evaluation_loop already patched")
return
# Check if the patterns exist
@@ -84,7 +84,7 @@ def patch_evaluation_loop():
)
exec(evaluation_loop_source, globals())
LOG.info("Patched Trainer.evaluation_loop with nanmean loss calculation")
LOG.debug("Patched Trainer.evaluation_loop with nanmean loss calculation")
Trainer.evaluation_loop = axolotl_evaluation_loop
@@ -135,5 +135,5 @@ def patch_maybe_log_save_evaluate():
)
exec(maybe_log_source, globals())
LOG.info("Patched Trainer._maybe_log_save_evaluate with nanmean loss calculation")
LOG.debug("Patched Trainer._maybe_log_save_evaluate with nanmean loss calculation")
Trainer._maybe_log_save_evaluate = axolotl_maybe_log_save_evaluate

3
src/axolotl/train.py
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@@ -196,10 +196,11 @@ def execute_training(
)
)
LOG.info("Starting trainer...")
# TODO: disabling for now as not compatible with FSDP2 + torchao low bit optimizers
# if cfg.bf16:
# torch.set_default_dtype(torch.bfloat16)
LOG.info("Starting trainer...")
trainer.train(resume_from_checkpoint=resume_from_checkpoint)
plugin_manager = PluginManager.get_instance()

9
src/axolotl/utils/__init__.py
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@@ -44,15 +44,6 @@ def set_pytorch_cuda_alloc_conf():
)
def patch_optimized_env():
"""
Patch environment variables to improve VRAM usage and increase download speed
"""
if os.getenv("HF_HUB_ENABLE_HF_TRANSFER") is None:
os.environ["HF_HUB_ENABLE_HF_TRANSFER"] = "1"
set_pytorch_cuda_alloc_conf()
def get_not_null(value, default=None):
"""
return the value if it's not None, otherwise return the default value

7
src/axolotl/utils/logging.py
View File

@@ -2,7 +2,6 @@
import functools
import logging
import os
from axolotl.utils.distributed import is_main_process
@@ -40,10 +39,6 @@ class MultiProcessAdapter(logging.LoggerAdapter):
def get_logger(name: str, log_level: str | None = None) -> MultiProcessAdapter:
if log_level is None:
log_level = os.environ.get("AXOLOTL_LOG_LEVEL", None)
logger = logging.getLogger(name)
if log_level is not None:
logger.setLevel(log_level.upper())
logger.root.setLevel(log_level.upper())
logger.setLevel(logging.DEBUG)
return MultiProcessAdapter(logger, extra={})

166
src/axolotl/utils/tee.py Normal file
View File

@@ -0,0 +1,166 @@
"""
Utilities for managing the debug log file and providing a file-only stream for logging
handlers.
"""
from __future__ import annotations
import io
import os
import sys
import threading
from pathlib import Path
from typing import TextIO, cast
_lock = threading.Lock()
_file_handle: io.TextIOWrapper | None = None
_log_path: str | None = None
_tee_installed: bool = False
_orig_stdout: TextIO | None = None
_orig_stderr: TextIO | None = None
class _FileOnlyWriter(io.TextIOBase):
"""A stream-like object that writes only to the tee file.
Before the file is prepared, writes are dropped (no-op).
"""
def write(self, s: str) -> int: # type: ignore[override]
with _lock:
if _file_handle is not None:
_file_handle.write(s)
return len(s)
return len(s)
def flush(self) -> None: # type: ignore[override]
with _lock:
if _file_handle is not None:
try:
_file_handle.flush()
except Exception:
pass
file_only_stream: io.TextIOBase = _FileOnlyWriter()
class _StreamTee(io.TextIOBase):
"""A minimal tee that mirrors writes to the debug log file.
Installed only after the debug log is prepared; no buffering.
"""
def __init__(self, stream: io.TextIOBase):
self._stream = stream
def write(self, s: str) -> int: # type: ignore[override]
with _lock:
n = self._stream.write(s)
if _file_handle is not None:
_file_handle.write(s)
return n
def flush(self) -> None: # type: ignore[override]
with _lock:
self._stream.flush()
if _file_handle is not None:
try:
_file_handle.flush()
except Exception:
pass
@property
def encoding(self): # type: ignore[override]
return getattr(self._stream, "encoding", None)
@property
def errors(self): # type: ignore[override]
return getattr(self._stream, "errors", None)
def isatty(self): # type: ignore[override]
return getattr(self._stream, "isatty", lambda: False)()
def fileno(self): # type: ignore[override]
if hasattr(self._stream, "fileno"):
return self._stream.fileno()
raise OSError("Underlying stream has no fileno")
def prepare_debug_log(cfg, filename: str = "debug.log") -> str:
"""
Prepare the debug log.
Creates the output directory, handles append/truncate logic based on cfg, and opens
the debug log file for subsequent writes via file-only handlers.
"""
global _file_handle, _log_path, _tee_installed
with _lock:
# If already initialized, reuse existing path
if _log_path is not None:
return _log_path
output_dir = cfg.output_dir
os.makedirs(output_dir, exist_ok=True)
log_path = Path(output_dir) / filename
append = bool(
cfg.get("resume_from_checkpoint") or cfg.get("auto_resume_from_checkpoints")
)
if not append and log_path.exists():
log_path.unlink()
fh = open(log_path, "a", encoding="utf-8")
fh.flush()
_file_handle = fh
_log_path = str(log_path)
# Install a tee so stdout/stderr are mirrored to the debug file
# Allow disabling via env for testing or advanced usage.
tee_enabled = os.getenv("AXOLOTL_TEE_STDOUT", "1").lower() not in {
"0",
"false",
"no",
}
if tee_enabled and not _tee_installed:
# Save originals so we can restore later (e.g., tests)
global _orig_stdout, _orig_stderr
_orig_stdout = sys.stdout
_orig_stderr = sys.stderr
sys.stdout = _StreamTee(cast(io.TextIOBase, sys.stdout))
sys.stderr = _StreamTee(cast(io.TextIOBase, sys.stderr))
_tee_installed = True
return _log_path
def close_debug_log() -> None:
"""Flush and close the debug log and uninstall the stdout/stderr tee.
Safe to call even if not initialized.
"""
global _file_handle, _log_path, _tee_installed, _orig_stdout, _orig_stderr
with _lock:
# Restore original stdout/stderr if we installed a tee
if _tee_installed:
if _orig_stdout is not None:
sys.stdout = _orig_stdout
if _orig_stderr is not None:
sys.stderr = _orig_stderr
_tee_installed = False
_orig_stdout = None
_orig_stderr = None
# Close the file handle if open
if _file_handle is not None:
try:
_file_handle.flush()
_file_handle.close()
except Exception:
pass
finally:
_file_handle = None
_log_path = None

4
src/axolotl/utils/train.py
View File

@@ -31,6 +31,7 @@ def determine_last_checkpoint(cfg: DictDefault, update: bool = True) -> str | No
if checkpoints:
last_checkpoint = str(checkpoints[-1])
if not update:
LOG.info(f"Resuming from last checkpoint at {last_checkpoint}")
return last_checkpoint
if (
@@ -40,6 +41,7 @@ def determine_last_checkpoint(cfg: DictDefault, update: bool = True) -> str | No
):
cfg.resume_from_checkpoint = last_checkpoint
LOG.info(
f"Using Auto-resume functionality to start with checkpoint at {cfg.resume_from_checkpoint}"
"Using auto-resume functionality to resume from checkpoint at "
f"{cfg.resume_from_checkpoint}"
)
return cfg.resume_from_checkpoint

9
src/axolotl/utils/trainer.py
View File

@@ -655,15 +655,6 @@ def prepare_optim_env(cfg):
os.environ["ACCELERATE_MIXED_PRECISION"] = "no"
def prepare_opinionated_env(cfg):
if cfg.qlora_sharded_model_loading:
# model loading is forked after the tokenizer
os.environ["TOKENIZERS_PARALLELISM"] = "false"
if cfg.sample_packing:
# multipack parallel packing sampler defaults to using fork
os.environ["TOKENIZERS_PARALLELISM"] = "false"
def setup_trainer(
cfg,
train_dataset,

103
tests/test_logging_config_file_capture.py Normal file
View File

@@ -0,0 +1,103 @@
import logging
import tempfile
import pytest
def read(path: str) -> str:
with open(path, "r", encoding="utf-8") as f:
return f.read()
@pytest.fixture(autouse=True)
def _reset_logging_state():
# Ensure a clean slate for logging between tests
for handler in logging.root.handlers[:]:
logging.root.removeHandler(handler)
logging.shutdown()
# Note: dictConfig in configure_logging will set up handlers again
yield
for handler in logging.root.handlers[:]:
logging.root.removeHandler(handler)
logging.shutdown()
def test_axolotl_logs_captured_at_all_levels(monkeypatch):
from axolotl.logging_config import configure_logging
from axolotl.utils import tee
from axolotl.utils.logging import get_logger
with tempfile.TemporaryDirectory() as td:
# Avoid stdout tee in this test to simplify interaction with pytest capture
monkeypatch.setenv("AXOLOTL_TEE_STDOUT", "0")
configure_logging()
path = tee.prepare_debug_log(
type("Cfg", (), {"output_dir": td, "get": lambda *_: False})
)
log = get_logger("axolotl.test")
log.info("AX-INFO")
log.debug("AX-DEBUG")
tee.file_only_stream.flush()
data = read(path)
assert "AX-INFO" in data
assert "AX-DEBUG" in data
tee.close_debug_log()
def test_third_party_logs_filtered_and_warning_captured(monkeypatch):
from axolotl.logging_config import configure_logging
from axolotl.utils import tee
with tempfile.TemporaryDirectory() as td:
monkeypatch.setenv("AXOLOTL_TEE_STDOUT", "0")
configure_logging()
path = tee.prepare_debug_log(
type("Cfg", (), {"output_dir": td, "get": lambda *_: False})
)
# Third-party logger (non-axolotl)
other = logging.getLogger("thirdparty.lib")
other.info("TP-INFO")
other.warning("TP-WARN")
# Simulate Python warnings routed through logging
logging.getLogger("py.warnings").warning("PY-WARN")
# Push through buffers
tee.file_only_stream.flush()
data = read(path)
# INFO from non-axolotl should be filtered out (not present)
assert "TP-INFO" not in data
# WARNING+ should be present
assert "TP-WARN" in data
# Python warnings captured (via py.warnings logger)
assert "PY-WARN" in data
tee.close_debug_log()
tee.close_debug_log()
def test_prepare_debug_log_idempotent_and_no_duplicate(monkeypatch):
from axolotl.logging_config import configure_logging
from axolotl.utils import tee
from axolotl.utils.logging import get_logger
with tempfile.TemporaryDirectory() as td:
monkeypatch.setenv("AXOLOTL_TEE_STDOUT", "0")
configure_logging()
cfg = type("Cfg", (), {"output_dir": td, "get": lambda *_: False})
p1 = tee.prepare_debug_log(cfg)
p2 = tee.prepare_debug_log(cfg)
assert p1 == p2
log = get_logger("axolotl.test")
marker = "UNIQUE-MARKER-12345"
log.info(marker)
tee.file_only_stream.flush()
data = read(p1)
# Ensure the marker appears once (not duplicated via propagation)
assert data.count(marker) == 1
tee.close_debug_log()

107
tests/test_utils_tee.py Normal file
View File

@@ -0,0 +1,107 @@
import os
import tempfile
def _dummy_cfg(output_dir: str, append: bool = False):
# Minimal object with attributes used by prepare_debug_log
class Cfg:
def __init__(self, out, append):
self.output_dir = out
self._append = append
def get(self, key, default=None):
if key in {"resume_from_checkpoint", "auto_resume_from_checkpoints"}:
return self._append
return default
return Cfg(output_dir, append)
def read(path: str) -> str:
with open(path, "r", encoding="utf-8") as f:
return f.read()
def test_file_only_stream_writes_after_prepare(monkeypatch):
from axolotl.utils import tee
with tempfile.TemporaryDirectory() as td:
# Avoid stdout tee in this test
monkeypatch.setenv("AXOLOTL_TEE_STDOUT", "0")
cfg = _dummy_cfg(td, append=False)
# before prepare: writing to file_only_stream creates no file
tee.file_only_stream.write("before\n")
tee.file_only_stream.flush()
assert not os.path.exists(os.path.join(td, "debug.log"))
# prepare and write
path = tee.prepare_debug_log(cfg)
assert os.path.basename(path) == "debug.log"
tee.file_only_stream.write("hello\n")
tee.file_only_stream.flush()
content = read(path)
assert "hello" in content
tee.close_debug_log()
def test_stdout_is_mirrored_after_prepare(capsys, monkeypatch):
from axolotl.utils import tee
with tempfile.TemporaryDirectory() as td:
cfg = _dummy_cfg(td, append=False)
try:
# Install tee while capture is disabled so stdout tee wraps real stdout.
with capsys.disabled():
monkeypatch.setenv("AXOLOTL_TEE_STDOUT", "1")
path = tee.prepare_debug_log(cfg)
import sys
print("printed-line")
sys.stdout.flush()
# Now verify file contains the line
content = read(path)
assert "printed-line" in content
finally:
tee.close_debug_log()
def test_truncate_vs_append_behavior(monkeypatch):
from axolotl.utils import tee
with tempfile.TemporaryDirectory() as td:
# Avoid stdout tee in this test
monkeypatch.setenv("AXOLOTL_TEE_STDOUT", "0")
# First run creates file with A
cfg = _dummy_cfg(td, append=False)
_ = tee.prepare_debug_log(cfg)
try:
tee.file_only_stream.write("A\n")
tee.file_only_stream.flush()
finally:
tee.close_debug_log()
# Second run with append=False truncates
cfg2 = _dummy_cfg(td, append=False)
path2 = tee.prepare_debug_log(cfg2)
try:
tee.file_only_stream.write("B\n")
tee.file_only_stream.flush()
content = read(path2)
assert "A\n" not in content and "B\n" in content
finally:
tee.close_debug_log()
# Third run with append=True preserves existing
cfg3 = _dummy_cfg(td, append=True)
path3 = tee.prepare_debug_log(cfg3)
try:
tee.file_only_stream.write("C\n")
tee.file_only_stream.flush()
content = read(path3)
assert "B\n" in content and "C\n" in content
finally:
tee.close_debug_log()