Python; 无法共享变量并在线程之间更新Qt GUI

Question

The integer variable defined in thread 1 does not want to share to thread 2, nor does the UI want to update on an simple loop to update it.

Main.py

from ui import Ui_main_window
from PyQt4 import QtGui, QtCore

import sys
import subprocess
import commands
import threading

class MainWindow(QtGui.QMainWindow, Ui_main_window):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.setupUi(self)

def _dd_thread_run(_if, _of, _bs, _size):
    _dd_subprocess_command_format = "dd if=%s bs=%s | pv -n --size %s | dd of=%s" % (_if, _bs, _size, _of)
    _dd_subprocess_command = [_dd_subprocess_command_format]
    _dd_progress = subprocess.Popen(_dd_subprocess_command, shell=True, stderr=subprocess.PIPE)
    while _dd_progress.poll() is None:
        out = _dd_progress.stderr.readline().replace("\n", "")
        out_int = int (out)
        print "[DEBUG] %r" % out_int

def _dd_do():
    _dd_thread_run("/dev/urandom", "/dev/null", "100K", "100M")

def _ui_progress_set():
    while True:
        for i in range(0, 100):
            ui2 = MainWindow()
            ui2.progressBar.setValue(i) # < Not working, does nothing, no error
            print out_int # < Throws error, "not defined"


app = QtGui.QApplication(sys.argv)

ui = MainWindow()
ui.show()

t1 = threading.Thread(target=_dd_do, args=[])
t1.start()

t2 = threading.Thread(target=_ui_progress_set, args=[])
t2.start()

sys.exit(app.exec_())

The program is pretty simple and straight forward. Have i missed something? How to handle a global variable to use between threads?

Upon starting the second thread, it immediately throws the error that out_int is not defined.

Exception in thread Thread-2:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 763, in run
    self.__target(*self.__args, **self.__kwargs)
  File "untitled3.py", line 55, in _ui_progress_set
    print out_int
NameError: global name 'out_int' is not defined

[DEBUG] 12
[DEBUG] 25
[DEBUG] 38
[DEBUG] 52
[DEBUG] 65
[DEBUG] 79
[DEBUG] 92
[DEBUG] 94

While it is, here: out_int = int (out)

But, as you can see, the integer is formatted correctly and printed to the console.

Answer 1

What you do is equivalent to:

#!/usr/bin/python

def first() :
  out_int = 1


def second() :
  print out_int

first()
second()

Which results in :

Traceback (most recent call last):
  File "./test.py", line 12, in <module>
    second()
  File "./test.py", line 8, in second
    print out_int
NameError: global name 'out_int' is not defined

So you have to define your out_int on the global scope and declare in the modifying function that you want to access that global variable.

The solution looks like:

#!/usr/bin/python

out_int = 0

def first() :
  global out_int
  out_int = 1


def second() :
  print out_int

first()
second()