MiniLogging.jl

Note

• v0.1 is last release that supports Julia v0.6.
• Users have to explicitly export logging macros because they are already used by Base.

  using MiniLogging
  # Explicitly shadow Base
  using MiniLogging: @debug, @info, @warn, @error, @critical

Overview

This is a Julia equivalent of Python logging package. It provides a basic hierarchical logging system.

Why another logging package?

When dealing with multiple nested modules, the experience with the existing Julia logging.jl package isn't very nice.

• To keep a logger hierarchy, I have to explicitly pass in a parent logger which might not exist yet.
• To change the current logging level, I have to find all descendant loggers and explicitly set them.

Features

• The logger hierarchy is defined by the logger name, which is a dot-separated string (e.g. "a.b").
  • Simply use get_logger(@__MODULE__) to maintain a hierarchy.
• All loggers inherit settings from their ancestors up to the root by default.
  • Most of the time it is sufficient to set the root logger config only.
• Colors & logging levels are customizable.

Exposed Verbs

export get_logger, basic_config
export @debug, @info, @warn, @error, @critical

Usage

julia> using MiniLogging
julia> using MiniLogging: @debug, @info, @warn, @error, @critical

# Get root logger.
# Nothing appears as we haven't set any config on any loggers.
julia> root_logger = get_logger()
RootLogger(WARN:30)

# This is also root logger.
julia> get_logger("")
RootLogger(WARN:30)

# Set root config.
# It inserts a handler that outputs message to `STDERR`.
julia> basic_config(MiniLogging.INFO)

# It changes the root logger level.
julia> get_logger("")
RootLogger(INFO:20)

julia> @warn(root_logger, "Hello", " world")
2016-11-21 17:31:50:WARN:Main:Hello world

# Get a logger.
julia> logger = get_logger("a.b")
Logger("a.b", NOTSET:0)

# Since the level of `logger` is unset, it inherits its nearest ancestor's level.
# Its effective level is `INFO` (from `root_logger`) now.
julia> @info(logger, "Hello", " world")
2016-11-21 16:41:46:INFO:a.b:Hello world

# Since `DEBUG < INFO`, no message is generated.
# Note the argument expressions are not evaluated in this case to increase performance.
julia> @debug(logger, "Hello", " world", error("no error"))

# Explicitly set the level.
# The error is triggered.
julia> logger.level = MiniLogging.DEBUG
julia> @debug(logger, "Hello", " world", error("has error"))
ERROR: has error
 in error(::String) at ./error.jl:21

# Get a child logger.
julia> logger2 = get_logger("a.b.c")
Logger("a.b.c", NOTSET:0)

# Its effective level now is `DEBUG` (from `logger`) now.
julia> @debug(logger2, "Hello", " world")
2016-11-21 17:34:38:DEBUG:a.b.c:Hello world

basic_config

• basic_config(level::LogLevel; date_format::String="%Y-%m-%d %H:%M:%S")
  • Log to STDERR.
• basic_config(level::LogLevel, file_name::String; date_format::String="%Y-%m-%d %H:%M:%S", file_mode::String="a")
  • Log to file_name.

# Log to both `STDERR` &  a file.
basic_config(MiniLogging.INFO, "foo")
root_logger = get_logger()
push!(root_logger.handlers, MiniLogging.Handler(stderr, "%Y-%m-%d %H:%M:%S”))

Add A New Level

julia> MiniLogging.define_new_level(:trace, 25, :yellow)
julia> @trace(logger, "Hello", " world")
2017-05-04 15:44:04:trace:a.b:Hello world