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Logging

In Mantid, logging can be used to issue messages that appear in a variety of places depending on the running environment. For example, in MantidWorkbench the Messages Box is used to display log messages to users and everything is also logged to a file.

The level of detail is controlled by right-clicking on the Messages Box in MantidWorkbench and selecting “log level”. Alternatively it can be controlled by the logging.loggers.root.level key in the properties file. There are several levels of logging available, ordered in terms of increasing priority:

• Debug

• Information - algorithm properteries are automatically logged at this level

• Notice - default level for users

• Warning

• Error - consider throwing an exception instead

Any log message that is sent at a priority level above or equal to the value set in the properties file will appear in the appropriate location, i.e. Messages Box, log file.

Within a Python algorithm the log can be accessed using self.log() which is a configured instance of the Logger. To post a message, simply choose a priority level and call a function that has that name with the message as an argument

def PyExec(self):
    param = self.getProperty("Inputvalue")

    self.log().information("The cube of the input value " +
                           str(param) + " is " + str(i*i*i))

Avoid excessive logging as it is an expensive operation, i.e. try to avoid posting a log message at every iteration through a loop as it can slow the algorithm down dramatically. Instead build the message up as the loop is traversed and call the logging function once

def PyExec(self):
    limit = self.getProperty('LoopLimit')
    sum = 0
    msg = ""
    for i in range(1, limit+1):
        sum += i*i
        msg += str(i*i) + ' '

    # This will be much more efficient,
    # especially if LoopLimit is large
    self.log().information(msg)

The logger only has ability to log strings. Therefore, construct your log messages as strings using string formatting.