Simple example of the correct way to use (Py)Qt(5) and QThread

threads1.py

# Copyright (c) 2016 Rob Kent (jazzycamel)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
# and associated documentation files (the "Software"), to deal in the Software without restriction, 
# including without limitation the rights to use, copy, modify, merge, publish, distribute, 
# sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all copies or 
# substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT 
# NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, 
# DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
from itertools import count, islice

class Threaded(QObject):
    result=pyqtSignal(int)

    def __init__(self, parent=None, **kwargs):
        super().__init__(parent, **kwargs)

    @pyqtSlot()
    def start(self): print("Thread started")

    @pyqtSlot(int)
    def calculatePrime(self, n):
        primes=(n for n in count(2) if all(n % d for d in range(2, n)))
        self.result.emit(list(islice(primes, 0, n))[-1])

class GUI(QWidget):
    requestPrime=pyqtSignal(int)

    def __init__(self, parent=None, **kwargs):
        super().__init__(parent, **kwargs)

        self._thread=QThread()
        self._threaded=Threaded(result=self.displayPrime)
        self.requestPrime.connect(self._threaded.calculatePrime)
        self._thread.started.connect(self._threaded.start)
        self._threaded.moveToThread(self._thread)
        qApp.aboutToQuit.connect(self._thread.quit)
        self._thread.start()

        l=QVBoxLayout(self)
        self._iterationLE=QLineEdit(self, placeholderText="Iteration (n)")
        l.addWidget(self._iterationLE)
        self._requestBtn=QPushButton(
            "Calculate Prime", self, clicked=self.primeRequested)
        l.addWidget(self._requestBtn)
        self._busy=QProgressBar(self)
        l.addWidget(self._busy)
        self._resultLbl=QLabel("Result:", self)
        l.addWidget(self._resultLbl)

    @pyqtSlot()
    def primeRequested(self):
        try: n=int(self._iterationLE.text())
        except: return
        self.requestPrime.emit(n)
        self._busy.setRange(0,0)
        self._iterationLE.setEnabled(False)
        self._requestBtn.setEnabled(False)

    @pyqtSlot(int)
    def displayPrime(self, prime):
        self._resultLbl.setText("Result: {}".format(prime))
        self._busy.setRange(0,100)
        self._iterationLE.setEnabled(True)
        self._requestBtn.setEnabled(True)

if __name__=="__main__":
    from sys import exit, argv

    a=QApplication(argv)
    g=GUI()
    g.show()
    exit(a.exec_())

And it's in our docs: https://pyqtgraph.readthedocs.io/en/latest/getting_started/qtcrashcourse.html#id8

Thanks!