# Logging¶

Brian uses a logging system to display warnings and general information messages to the user, as well as writing them to a file with more detailed information, useful for debugging. Each log message has one of the following “log levels”:

ERROR
Only used when an exception is raised, i.e. an error occurs and the current operation is interrupted. Example: You use a variable name in an equation that Brian does not recognize.
WARNING
Brian thinks that something is most likely a bug, but it cannot be sure. Example: You use a Synapses object without any synapses in your simulation.
INFO
Brian wants to make the user aware of some automatic choice that it did for the user. Example: You did not specify an integration method for a NeuronGroup and therefore Brian chose an appropriate method for you.
DEBUG
Additional information that might be useful when a simulation is not working as expected. Example: The integration timestep used during the simulation.
DIAGNOSTIC
Additional information useful when tracking down bugs in Brian itself. Example: The generated code for a CodeObject.

By default, all messages are written to the log file and all messages of level INFO and above are displayed on the console. To change what messages are displayed, see below.

Note

By default, the log file is deleted after a successful simulation run, i.e. when the simulation exited without an error. To keep the log around, set the logging.delete_log_on_exit preference to False.

## Showing/hiding log messages¶

If you want to change what messages are displayed on the console, you can call a method of the method of BrianLogger:

BrianLogger.log_level_debug() # now also display debug messages


It is also possible to suppress messages for certain sub-hierarchies by using BrianLogger.suppress_hierarchy:

# 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 BrianLogger.suppress_name:

# 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.

## Preferences¶

You can also change details of the logging system via Brian’s Preferences system. With this mechanism, you can switch the logging to a file off completely (by setting logging.file_log to False) or have it log less messages (by setting logging.file_log_level to a level higher than DIAGNOSTIC) – this can be important for long-running simulations where the log might otherwise take up a lot of disk space. For a list of all preferences related to logging, see the documentation of the brian2.utils.logger module.

Warning

Most of the logging preferences are only taken into account during the initialization of the logging system which takes place as soon as brian2 is imported. Therefore, if you use e.g. prefs.logging.file_log = False in your script, this will not have the intended effect! Instead, set these preferences in a file (see Preferences).