test.py

import time

print('start')

for i in range(10):
    print(i)
    time.sleep(1)

print('stop')

textedit.py

class PythonProcessPane(QTextEdit):
    """
    Captures, displays and works with the stdin, stdout and stderr of a Python
    process.

    Used for running standard Python3 scripts.
    """

    def start_process(self, script):
        self.script = script
        logger.info('Running script: {}'.format(script))
        self.process = QProcess(self)
        self.process.readyRead.connect(self.read)
        self.process.start('python3', [script])

    def append(self, byte_stream):
        """
        Append text to the text area.
        """
        cursor = self.textCursor()
        cursor.movePosition(cursor.End)
        cursor.insertText(byte_stream.data().decode('utf-8'))

    def read(self):
        """
        From the process's stdout.
        """
        self.append(self.process.readAll())