Logging in Brian is based on the
logging module in Python’s standard
library. In Brian, all logging output is logged to a file (the file name is
brian2.utils.logger.TMP_LOG). This log file will normally be
deleted on exit, except if an uncaught exception occured or if
logging.delete_log_on_exit is set to
False. The default log level for the
logging on the console is “warn”.
logger = get_logger(__name__)
In the code, logging can then be done via:
logger.debug('A debug message') logger.info('An info message') logger.warn('A warning message') logger.error('An error message')
If a module logs similar messages in different places or if it might be useful to be able to suppress a subset of messages in a module, add an additional specifier to the logging command, specifying the class or function name, or a method name including the class name (do not include the module name, it will be automatically added as a prefix):
logger.debug('A debug message', 'CodeString') logger.debug('A debug message', 'NeuronGroup.update') logger.debug('A debug message', 'reinit')
If you want to log a message only once, e.g. in a function that is called
repeatedly, set the optional
once keyword to
logger.debug('Will only be shown once', once=True) logger.debug('Will only be shown once', once=True)
The output of debugging looks like this in the log file:
2012-10-02 14:41:41,484 DEBUG brian2.equations.equations.CodeString: A debug message
and like this on the console (if the log level is set to “debug”):
DEBUG brian2.equations.equations.CodeString: A debug message
Log level recommendations¶
- Low-level messages that are not of any interest to the normal user but useful for debugging. A typical example is the source code generated by the code generation module.
- Messages that are not necessary for the user, but possibly helpful in understanding the details of what is going on. An example would be displaying a message about which stateupdater has been chosen automatically after analyzing the equations, when no stateupdater has been specified explicitly.
- Messages that alert the user to a potential mistake in the code, e.g. two
possible solutions for an identifier in an equation. It can also be used to
make the user aware that he/she is using an experimental feature, an
unsupported compiler or similar. In this case, normally the
once=Trueoption should be used to raise this warning only once. As a rule of thumb, “common” scripts like the examples provided in the examples folder should normally not lead to any warnings.
- This log level is not used currently in Brian, an exception should be raised instead. It might be useful in “meta-code”, running scripts and catching any errors that occur.
Showing/hiding log messages¶
The user can change the level of displayed log messages by using a static
BrianLogger.log_level_info() # now also display info messages
It is also possible to suppress messages for certain sub-hierarchies by using
# Suppress code generation messages on the console BrianLogger.suppress_hierarchy('brian2.codegen') # Suppress preference messages even in the log file BrianLogger.suppress_hierarchy('brian2.core.preferences', filter_log_file=True)
Similarly, messages ending in a certain name can be suppressed with
# Suppress resolution conflict warnings BrianLogger.suppress_name('resolution_conflict')
These functions should be used with care, as they suppresses messages independent of the level, i.e. even warning and error messages.
Testing log messages¶
It is possible to test whether code emits an expected log message using the
catch_logs context manager. This is normally not
necessary for debug and info messages, but should be part of the unit tests
for warning messages (
catch_logs by default only catches
warning and error messages):
with catch_logs() as logs: # code that is expected to trigger a warning # ... assert len(logs) == 1 # logs contains tuples of (log level, name, message) assert logs == 'WARNING' and logs.endswith('warning_type')