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Outputs and Logging

The Aries.output module provides classes and methods for configuring logging and capturing outputs from python function or method.

Logging Configurations

To configure logging, simply call LoggingConfig.enable() as follows:

import logging
from Aries.outputs import LoggingConfig

LoggingConfig().enable()
logger = logging.getLogger(__name__)

This will enable logging using the default logging message format.

The default logging format is:

'%(asctime)s | %(levelname)-8s | %(lineno)4d@%(module)-15s | %(message)s'

which produces logging messages like:

2019-09-29 22:57:03 | DEBUG    |   53@atest_outputs   | Test Config Debug

The line number and module name is useful for identifying the location of the logging code.

You can customize the logging format by passing a python logging Formatter or a logging format string. Logging format string generally contain placeholders of log record attributes. For more information about python logging format string. For more information, see Python Log Record Attributes.

Use the formatter argument to customize the formatter:

LoggingConfig(formatter='%(message)s').enable()
logger = logging.getLogger(__name__)

The __name__ in variable is a special built-in variable containing the name of the module, e.g.(Aries.outputs). This is usually used as the name of the logger. However, you can replace it with your own string to name/organize your logging. This corresponds to the %(name)s attribute in a log record.

By default LoggingConfig().enable() changes the log level to DEBUG. You can modify this by passing a level argument.

LoggingConfig(level=logging.INFO).enable()

You may also want to output only the log messages from certain packages, for example, your own package. This can be done by using the packages argument, which accepts a list of strings.

LoggingConfig(packages=["tests"]).enable()

The above code configures the logging to handle only logs from "tests" package.

To remove the logging configuration, save the object returned by enable() and call the disable() method.

config = LoggingConfig().enable()
# ...
# YOUR CODE HERE
# ...
config.disable()

Additionally, LoggingConfig also provides context manager and decorator for handling loggings for a particular part of your code.

Context Manager, logging configuration will be effective only inside "with":

with LoggingConfig():
    # Customized logging in this block only
    logger = logging.getLogger(__name__)
    # ...
    # YOUR CODE HERE
    # ...

# Logging will be restored/removed from here

Decorator, logging configuration will only be effective for the function:

@LoggingConfig.decorate
def your_function(*args, **kwargs):
    logger = logging.getLogger(__name__)
    # ...
    # YOUR CODE HERE
    # ...

Capturing Outputs

The CaptureOutput class provides an easy way to capture the outputs and loggings of your code into variables.

from Aries.outputs import CaptureOutput

with CaptureOutput() as out:
    do_something()

# The standard outputs, standard errors, logs and exception outputs (if any) 
# are saved as strings (with line breaks)
standard_outputs = out.std_out
standard_errors = out.std_err
log_messages = out.log_out
exceptions = out.exc_out

In multi-threading programs, CaptureOutput saves only the logs of the current thread running the code. However, since multiple threads are sharing the same standard output/error, the std_out and std_err will contain the outputs/errors from all threads in the same process. To capture the stdout/stderr of a particular thread, run the thread in an independent process.