Refined Qt GUI example in the logging cookbook. (pythonGH-15045)

Author: vsajip

Doc/howto/logging-cookbook.rst

@@ -2760,16 +2760,16 @@ The following example shows how to log to a Qt GUI. This introduces a simple
 ``QtHandler`` class which takes a callable, which should be a slot in the main
 thread that does GUI updates. A worker thread is also created to show how you
 can log to the GUI from both the UI itself (via a button for manual logging)
-as well as a worker thread doing work in the background (here, just random
-short delays).
+as well as a worker thread doing work in the background (here, just logging
+messages at random levels with random short delays in between).
 
 The worker thread is implemented using Qt's ``QThread`` class rather than the
 :mod:`threading` module, as there are circumstances where one has to use
 ``QThread``, which offers better integration with other ``Qt`` components.
 
 The code should work with recent releases of either ``PySide2`` or ``PyQt5``.
 You should be able to adapt the approach to earlier versions of Qt. Please
-refer to the comments in the code for more detailed information.
+refer to the comments in the code snippet for more detailed information.
 
 .. code-block:: python3
 
@@ -2789,22 +2789,24 @@ refer to the comments in the code for more detailed information.
  Signal = QtCore.pyqtSignal
  Slot = QtCore.pyqtSlot
 
+
  logger = logging.getLogger(__name__)
 
+
  #
  # Signals need to be contained in a QObject or subclass in order to be correctly
  # initialized.
  #
  class Signaller(QtCore.QObject):
- signal = Signal(str)
+ signal = Signal(str, logging.LogRecord)
 
  #
  # Output to a Qt GUI is only supposed to happen on the main thread. So, this
  # handler is designed to take a slot function which is set up to run in the main
- # thread. In this example, the function takes a single argument which is a
- # formatted log message. You can attach a formatter instance which formats a
- # LogRecord however you like, or change the slot function to take some other
- # value derived from the LogRecord.
+ # thread. In this example, the function takes a string argument which is a
+ # formatted log message, and the log record which generated it. The formatted
+ # string is just a convenience - you could format a string for output any way
+ # you like in the slot function itself.
  #
  # You specify the slot function to do whatever GUI updates you want. The handler
  # doesn't know or care about specific UI elements.
@@ -2817,7 +2819,7 @@ refer to the comments in the code for more detailed information.
 
  def emit(self, record):
  s = self.format(record)
- self.signaller.signal.emit(s)
+ self.signaller.signal.emit(s, record)
 
  #
  # This example uses QThreads, which means that the threads at the Python level
@@ -2827,6 +2829,13 @@ refer to the comments in the code for more detailed information.
  def ctname():
  return QtCore.QThread.currentThread().objectName()
 
+
+ #
+ # Used to generate random levels for logging.
+ #
+ LEVELS = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR,
+ logging.CRITICAL)
+
  #
  # This worker class represents work that is done in a thread separate to the
  # main thread. The way the thread is kicked off to do work is via a button press
@@ -2851,7 +2860,8 @@ refer to the comments in the code for more detailed information.
  while not QtCore.QThread.currentThread().isInterruptionRequested():
  delay = 0.5 + random.random() * 2
  time.sleep(delay)
- logger.debug('Message after delay of %3.1f: %d', delay, i, extra=extra)
+ level = random.choice(LEVELS)
+ logger.log(level, 'Message after delay of %3.1f: %d', delay, i, extra=extra)
  i += 1
 
  #
@@ -2864,10 +2874,18 @@ refer to the comments in the code for more detailed information.
  #
  class Window(QtWidgets.QWidget):
 
+ COLORS = {
+ logging.DEBUG: 'black',
+ logging.INFO: 'blue',
+ logging.WARNING: 'orange',
+ logging.ERROR: 'red',
+ logging.CRITICAL: 'purple',
+ }
+
  def __init__(self, app):
  super(Window, self).__init__()
  self.app = app
- self.textedit = te = QtWidgets.QTextEdit(self)
+ self.textedit = te = QtWidgets.QPlainTextEdit(self)
  # Set whatever the default monospace font is for the platform
  f = QtGui.QFont('nosuchfont')
  f.setStyleHint(f.Monospace)
@@ -2880,7 +2898,7 @@ refer to the comments in the code for more detailed information.
  self.handler = h = QtHandler(self.update_status)
  # Remember to use qThreadName rather than threadName in the format string.
  fs = '%(asctime)s %(qThreadName)-12s %(levelname)-8s %(message)s'
- formatter = logging.Formatter(f)
+ formatter = logging.Formatter(fs)
  h.setFormatter(formatter)
  logger.addHandler(h)
  # Set up to terminate the QThread when we exit
@@ -2932,21 +2950,25 @@ refer to the comments in the code for more detailed information.
  # that's where the slots are set up
 
  @Slot(str)
- def update_status(self, status):
- self.textedit.append(status)
+ def update_status(self, status, record):
+ color = self.COLORS.get(record.levelno, 'black')
+ s = '<pre><font color="%s">%s</font></pre>' % (color, status)
+ self.textedit.appendHtml(s)
 
  @Slot()
  def manual_update(self):
- levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR,
- logging.CRITICAL)
- level = random.choice(levels)
+ # This function uses the formatted message passed in, but also uses
+ # information from the record to format the message in an appropriate
+ # color according to its severity (level).
+ level = random.choice(LEVELS)
  extra = {'qThreadName': ctname() }
  logger.log(level, 'Manually logged!', extra=extra)
 
  @Slot()
  def clear_display(self):
  self.textedit.clear()
 
+
  def main():
  QtCore.QThread.currentThread().setObjectName('MainThread')
  logging.getLogger().setLevel(logging.DEBUG)