logging.rst

Logging

OpenStructure has a logging system going beyond what print statements can offer. Messages can be logged to the terminal to the graphical user interface or a file. Depending on the needs, groups of messages can be turned and off.

Note

In C++, the logging facility is implemented as a set of macros, called LOG_ERROR, LOG_WARNING, LOG_SCRIPT, LOG_INFO, LOG_VERBOSE, LOG_DEBUG and LOG_TRACE. The last two are only active when compiling with debugging symbols. When debugging symbols are off, they expand to an empty macro and thus don't create any overhead.

Verbosity Level

You can change the verbosity level with the following two methods:

Enumerates the logging levels (see :ref:`picking-logging-level`). Values:

Error, Warning, Script, Info, Verbose, Debug, Trace

Log sinks

When running OpenStructure from the command-line, the log messages are by default output to stderr. When running DNG, the log messages are additionally logged to the messages widget. However, it is also possible to log into a file or theoretically even to a remote computer. All these are instances of so-called log sinks: classes that derive from LogSink and implement the LogMessage method.

For convenience, there are 3 LogSink implementations available in OpenStructure that are sufficient for most use cases.

The FileLogSink logs all messages into the given file.

param filename:	The filename
type filename:	:class:`str`

The stream log sink writes all log messages to the stream. stream must have a write method that accepts a string. To write messages to stderr, use

stderr_sink=ost.StreamLogSink(sys.stderr)
ost.PushLogSink(stderr_sink)
ost.LogInfo('Welcome, master')

A LogSink for multiplexing the log messages into multiple sinks at the same time, e.g. the terminal and the messages widget.

To change the current log sink you can use the following methods:

Guidelines for picking logging level

Each logging event has an associated level that marks its importance. For example, users should always see errors, but they do not need to see detailed information on the loading process. Here is a list of guidelines that we use in the code. We encourage developers to adhere to these guidelines as closely as possible.

Error:

Very important message to the user, some command did not complete as expected or was aborted.

Warning:

Diagnose potential problems that do not abort the execution, but may point to a misconfiguration/misuse. This level is turned on by default.

Script:

Logging level that should be used from scripts, e.g. to report progress. These logging messages are turned on by default.

Info:

Informative and important messages that summarize a complex command, such as information on a loaded file, or results from an algorithm. These logging messages are not turned on by default.

Verbose:

Grey-zone between user and developer need, and perhaps the hardest to get right. This is the lowest logging level users will be able to see when they use an optimized build. An example for this is the OpenGL setup/info in gfx, or the path search during startup, or more detailed info on file IO. These messages are not turned on by default.

Debug:

For developers, but not quite at the trace level. This level is turned off by default, not available in Python and only enabled when compiling with debugging symbols.

Trace:

Used to debug inner loops. Once turned on, you will probably get more debug output that you will be able to handle. This level is turned off by default, not available in python and only enabled when compiling with debugging symbols.

Example

The following snippet explains how to create a custom log sink which logs to the terminal (or the python shell in DNG). The logger also prints the current time.

import datetime
class PyLogger(ost.LogSink):
  def __init__(self):
    ost.LogSink.__init__(self)

  def LogMessage(self, message, severity):
    levels=['ERROR', 'WARNING', 'SCRIPT', 'INFO',
            'VERBOSE', 'DEBUG', 'TRACE']
    level=levels[severity]
    print '%s[%s]: %s' % (level, str(datetime.datetime.now()), message),

py_logger=PyLogger()
ost.PushLogSink(py_logger)

ost.LogInfo("amazing logging system")