pyqtgraph dynamic plot: add line to open GUI - python-3.x

Question

I am trying to add new lines to an existing and open Plot.
I wrote a watchdog watching a folder with measurement data. Every few secs there will be a new data file. The Application I try to generate should read the file when triggered by the watchdog and add the data to the plot.
Dynamic plots using QTimer and stuff is easy when updating existing data, but I don't get a hook for new lines.
Also, do I have to use multithreading when I want to run a script while having a plot on _exec()?
from pyqtgraph.Qt import QtGui, QtCore
import pyqtgraph as pq
import sys
import numpy as np
import time
class Plot2d(object):
def __init__(self):
self.traces = dict()
self.num = 0
pq.setConfigOptions(antialias=True)
self.app = QtGui.QApplication(sys.argv)
self.win = pq.GraphicsWindow(title='examples')
self.win.resize(1000, 600)
self.win.setWindowTitle('Windowtitle')
self.canvas = self.win.addPlot(title='Plot')
def starter(self):
if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
QtGui.QApplication.instance().exec_()
def trace(self, name, dataset_x, dataset_y):
if name in self.traces:
self.traces[name].setData(dataset_x, dataset_y)
else:
self.traces[name] = self.canvas.plot(pen='y')
def update(self, i):
x_data = np.arange(0, 3.0, 0.01)
y_data = x_data*i
self.trace(str(i), x_data, y_data)
self.trace(str(i), x_data, y_data)
if __name__ == '__main__':
p = Plot2d()
p.update(1)
p.starter()
time.sleep(1)
p.update(2)
This is what I tried. The update function should be called by the watchdog when new data is available in the dir.
import time as time
from watchdog.observers import Observer
from watchdog.events import PatternMatchingEventHandler
if __name__ == "__main__":
patterns = "*"
ignore_patterns = ""
ignore_directories = False
case_sensitive = True
go_recursively = False
my_event_handler = PatternMatchingEventHandler(patterns, ignore_patterns, ignore_directories, case_sensitive)
def on_created(event):
print(f" {event.src_path} has been created!") #this function should call the plot update
my_event_handler.on_created = on_created
path = (r'C:\Users\...') #path from GUI at some point
my_observer = Observer()
my_observer.schedule(my_event_handler, path, recursive=go_recursively)
my_observer.start()
try:
while True:
time.sleep(1)
except KeyboardInterrupt:
my_observer.stop()
my_observer.join()

Answer 1

The exec_() method is blocking, so starter() will be too, and will be unlocked when the window is closed, which implies that all the code after starter will only be executed after closing the window. On the other hand you should not use time.sleep in the GUI thread as it blocks the execution of the GUI event loop.
Depending on the technology used, ways of updating elements are offered, in the case of Qt the appropriate way is to use signals so that all the logic of the watchdog will be encapsulated in a QObject that will transmit the information to the GUI through a signal, Then the GUI takes that information to plot.
import sys
from watchdog.observers import Observer
from watchdog.events import PatternMatchingEventHandler
from pyqtgraph.Qt import QtGui, QtCore
import pyqtgraph as pq
import numpy as np
class QObserver(QtCore.QObject):
dataChanged = QtCore.pyqtSignal(object)
def __init__(self, parent=None):
super(QObserver, self).__init__(parent)
patterns = "*"
ignore_patterns = ""
ignore_directories = False
case_sensitive = True
go_recursively = False
path = r"C:\Users\..." # path from GUI at some point
event_handler = PatternMatchingEventHandler(
patterns, ignore_patterns, ignore_directories, case_sensitive
)
event_handler.on_created = self.on_created
self.observer = Observer()
self.observer.schedule(event_handler, path, recursive=go_recursively)
self.observer.start()
def on_created(self, event):
print(
f" {event.src_path} has been created!"
) # this function should call the plot update
self.dataChanged.emit(np.random.randint(1, 5))
class Plot2d(QtCore.QObject):
def __init__(self, parent=None):
super().__init__(parent)
self.traces = dict()
self.num = 0
pq.setConfigOptions(antialias=True)
self.app = QtGui.QApplication(sys.argv)
self.win = pq.GraphicsWindow(title="examples")
self.win.resize(1000, 600)
self.win.setWindowTitle("Windowtitle")
self.canvas = self.win.addPlot(title="Plot")
def starter(self):
if (sys.flags.interactive != 1) or not hasattr(QtCore, "PYQT_VERSION"):
QtGui.QApplication.instance().exec_()
def trace(self, name, dataset_x, dataset_y):
if name in self.traces:
self.traces[name].setData(dataset_x, dataset_y)
else:
self.traces[name] = self.canvas.plot(pen="y")
#QtCore.pyqtSlot(object)
def update(self, i):
x_data = np.arange(0, 3.0, 0.01)
y_data = x_data * i
self.trace(str(i), x_data, y_data)
self.trace(str(i), x_data, y_data)
if __name__ == "__main__":
p = Plot2d()
qobserver = QObserver()
qobserver.dataChanged.connect(p.update)
p.starter()