File Logging

Basic File Sink

from logly import logger

# Simple file sink
logger.add("app.log", level="INFO")
logger.info("This goes to app.log")

TIP

By default, Logly creates the file if it doesn't exist and appends to it.

Custom Encoding

logger.add("app.log", encoding="utf-8")
logger.add("legacy.log", encoding="latin-1")

Binary streams are adapted the same way: logger.add(open("app.log", "w+b")) decodes with encoding (default "utf-8") without ever closing your object. Non-UTF-8 encodings cannot be combined with rotation, retention, compression, delay, or watch.

File Modes

# Append mode (default)
logger.add("app.log", mode="a")

# Write mode (truncate on open)
logger.add("app.log", mode="w")

Custom Opener

Use the opener parameter to customize how files are opened (e.g., for custom permissions):

import os


def custom_opener(path, flags):
    # An opener receives the path and os.open-style flags and returns a
    # file descriptor.
    return os.open(path, flags, 0o644)


logger.add("app.log", opener=custom_opener)

INFO

A custom opener, non-default buffering, or non-UTF-8 encoding opens the file in Python, so it cannot be combined with rotation, retention, compression, delay, or watch, which require the native file sink.

Delay Opening

# Don't open the file until the first message is logged
logger.add("app.log", delay=True)

Combining with Rotation

logger.add(
    "app.log",
    level="INFO",
    rotation="100 MB",
    retention="30 days",
    compression="gzip",
    encoding="utf-8",
    mode="a",
)

Using root_dir

Set a default root directory so all file paths are relative to it:

logger.root_dir("/var/log/myapp")
logger.add("app.log")  # Creates /var/log/myapp/app.log
logger.add("errors.log", level="ERROR")  # Creates /var/log/myapp/errors.log

INFO

root_dir() creates the directory if it doesn't exist.