PyInstaller-built Windows EXE fails with multiprocessing

Enabling --onedir multiprocessing support on Windows (does NOT work with --onefile on Windows, but otherwise safe on all platforms/configurations):

if __name__ == '__main__':
    # On Windows calling this function is necessary.
    multiprocessing.freeze_support()

Enabling --onefile multiprocessing support on Windows (safe on all platforms/configurations, compatible with --onedir):

import multiprocessing.forking
import os
import sys

class _Popen(multiprocessing.forking.Popen):
    def __init__(self, *args, **kw):
        if hasattr(sys, 'frozen'):
            # We have to set original _MEIPASS2 value from sys._MEIPASS
            # to get --onefile mode working.
            os.putenv('_MEIPASS2', sys._MEIPASS)
        try:
            super(_Popen, self).__init__(*args, **kw)
        finally:
            if hasattr(sys, 'frozen'):
                # On some platforms (e.g. AIX) 'os.unsetenv()' is not
                # available. In those cases we cannot delete the variable
                # but only set it to the empty string. The bootloader
                # can handle this case.
                if hasattr(os, 'unsetenv'):
                    os.unsetenv('_MEIPASS2')
                else:
                    os.putenv('_MEIPASS2', '')

class Process(multiprocessing.Process):
    _Popen = _Popen

# ...

if __name__ == '__main__':
    # On Windows calling this function is necessary.
    multiprocessing.freeze_support()

    # Use your new Process class instead of multiprocessing.Process

References
https://stackoverflow.com/questions/24944558/pyinstaller-built-windows-exe-fails-with-multiprocessing

Hide the console while using os.system or subprocess.call in Python

si = subprocess.STARTUPINFO()
si.dwFlags |= subprocess.STARTF_USESHOWWINDOW
#si.wShowWindow = subprocess.SW_HIDE # default
subprocess.call('taskkill /F /IM exename.exe', startupinfo=si)
CREATE_NO_WINDOW = 0x08000000
subprocess.call('taskkill /F /IM exename.exe', creationflags=CREATE_NO_WINDOW)
DETACHED_PROCESS = 0x00000008
subprocess.call('taskkill /F /IM exename.exe', creationflags=DETACHED_PROCESS)

References
https://stackoverflow.com/questions/7006238/how-do-i-hide-the-console-when-i-use-os-system-or-subprocess-call

Encoding of readAllStandardOutput() QProcess

    ...
    output = bytearray(self.process.readAllStandardOutput())
    output = output.decode(self.GetCMD_Encoding())
    print (output)

def GetCMD_Encoding(self):

    CMD = QProcess(self)
    CMD.setProcessChannelMode(QProcess.MergedChannels)
    CMD.start("C:\Windows\System32\chcp.com")
    CMD.waitForReadyRead()
    output = bytearray(CMD.readAllStandardOutput())
    output = output.decode("ascii")
    output = output[18:]
    return "cp" + output

References
https://stackoverflow.com/questions/41761132/pyqt-qprocess-readallstandardoutput-encoding
https://stackoverflow.com/questions/57663191/how-to-convert-a-qbytearray-to-a-python-string-in-pyside2

Get return value and PID of spawned process using QProcess

import sys
from PyQt4 import QtGui, QtCore
from PyQt4.QtCore import QProcess

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)

    command = "./testCommand.py"
    args = [""]

    #"regular" startDetached : give two arguments, get a boolean
    process=QProcess()
    re=process.startDetached("ls",["."])
    print(re)
    print(type(re))

    #"overload" startDetached : give three arguments, get a tuple(boolean,PID)
    process2=QProcess()
    re,pid=process2.startDetached("ls",["."],".")
    print(re,pid)
    print(type(re),type(pid))

References
https://stackoverflow.com/questions/31519215/pyqt4-qprocess-startdetached-cant-get-return-value-and-pid-of-spawned-proce

Use QProcess to run a program

if self.mosquitto_process is None:
    self.mosquitto_process = QProcess()
self.mosquitto_process.start("mosquitto.cmd")
self.port = utils.pick_free_port()
    _logger().debug('starting server process: %s',
                    ' '.join([self._interpreter, server.__file__,
                              str(self.port)]))
    self._process = QtCore.QProcess()
    self._process.readyRead.connect(self._on_ready_read)
    self._process.setProcessChannelMode(self._process.MergedChannels)
    self._process.finished.connect(self._on_finished)
    self._process.stateChanged.connect(self._on_state_changed)
    self._process.start(
        self._interpreter, (server.__file__, str(self.port)))

proc = QProcess()
    proc.start(*py_proc('print("Hello World")'))
    dev = qtutils.PyQIODevice(proc)
    assert not dev.closed
    with pytest.raises(OSError) as excinfo:
        dev.seek(0)
    assert str(excinfo.value) == 'Random access not allowed!'
    with pytest.raises(OSError) as excinfo:
        dev.tell()
    assert str(excinfo.value) == 'Random access not allowed!'
    proc.waitForFinished(1000)
    proc.kill()
    assert bytes(dev.read()).rstrip() == b'Hello World'

References
https://programtalk.com/python-examples/PyQt5.QtCore.QProcess/

Python timestamp to datetime and vice-versa

Python timestamp to datetime

from datetime import datetime

timestamp = 1545730073
dt_object = datetime.fromtimestamp(timestamp)

print("dt_object =", dt_object)
print("type(dt_object) =", type(dt_object))

Python datetime to timestamp

from datetime import datetime

# current date and time
now = datetime.now()

timestamp = datetime.timestamp(now)
print("timestamp =", timestamp)

References
https://www.programiz.com/python-programming/datetime/timestamp-datetime