I have recently started to delve into multiprocessing, as I believe my code can be easily parallelized. Upon working through the tutorials, though, I encountered an issue: functions distributed in a pool do not seem to print.
Here's the culprit:
__spec__ = None # This line is required for Spyder and not part of the actual example
from multiprocessing import Process
import os
def info(title):
print(title)
print('module name:', __name__)
print('parent process:', os.getppid())
print('process id:', os.getpid())
def f(name):
info('function f')
print('hello', name)
if __name__ == '__main__':
info('main line')
p = Process(target=f, args=('bob',))
p.start()
p.join()
The output I receive is the following:
main line
module name: __main__
parent process: 10812
process id: 11348*
Now it is clear that the console only seems to print the info function, but not any output of the f function (which is using multiprocessing.Process). I have encountered similar issues with other examples I found online: computations are done and returned correctly when using multiprocessing, but prints never show up in the console.
Does anybody know why, and how to address this issue?
On a possibly related note, I am using Python 3.6 in Spyder 3.2.4 . Spyder seems to have a few quirks, as the first line in the code already is a workaround required to allow multiprocessing to work at all, an issue I found already discussed here. A similar, unresolved issue was mentioned here.
I would appreciate any help, and a happy new year to everyone.
(Spyder maintainer here) Multiprocessing doesn't work well on Windows in Spyder's IPython console. However, you can run your code in an external terminal to have the results you want.
To do that, please go to
Run > Configuration per file > Execute in an external system terminal.
Update: Since our 5.2.0 version (released in November 2021), prints generated while running multiprocessing code are captured and displayed in the IPython console for all operating systems.
You can run it through Spyders' IPython console by saving the function as a different .py file and importing it into the script you're running. For example, save:
def f(name):
info('function f')
print('hello', name)
In a file called worker.py. Then in your main file, do the following:
from multiprocessing import Process
import os
import worker
def info(title):
print(title)
print('module name:', __name__)
print('parent process:', os.getppid())
print('process id:', os.getpid())
if __name__ == '__main__':
info('main line')
p = Process(target=worker.f, args=('bob',))
p.start()
p.join()
you can use log file instead. using fp.write()
Related
I have a code that is architecturally close to posted below (unfortunately i can't post full version cause it's proprietary). I have an self-updating executable and i'm trying to test this feature. We assume that full path to this file will be in A.some_path after executing input. My problem is that assertion failed, because on second call os.stat still returning the previous file stats (i suppose it thinks that nothing could changed so it's unnecessary). I have tried to launch this manually and self-updating works completely fine and the file is really removing and recreating with stats changing. Is there any guaranteed way to force os.stat re-read file stats by the same path, or alternative option to make it works (except recreating an A object)?
from pathlib import Path
import unittest
import os
class A:
some_path = Path()
def __init__(self, _some_path):
self.some_path = Path(_some_path)
def get_path(self):
return self.some_path
class TestKit(unittest.TestCase):
def setUp(self):
pass
def check_body(self, a):
some_path = a.get_path()
modification_time = os.stat(some_path).st_mtime
# Launching self-updating executable
self.assertTrue(modification_time < os.stat(some_path).st_mtime)
def check(self):
a = A(input('Enter the file path\n'))
self.check_body(a)
def Tests():
suite = unittest.TestSuite()
suite.addTest(TestKit('check'))
return suite
def main():
tests_suite = Tests()
unittest.TextTestRunner().run(tests_suite)
if __name__ == "__main__":
main()
I have found the origins of the problem: i've tried to launch self-updating via os.system which wait till the process done. But first: during the self-updating we launch several detached proccesses and actually should wait unitl all them have ended, and the second: even the signal that the proccess ends doesn't mean that OS really completely realease the file, and looks like on assertTrue we are not yet done with all our routines. For my task i simply used sleep, but normal solution should analyze the existing proccesses in the system and wait for them to finish, or at least there should be several attempts with awaiting.
I'm so curious about this and need some advise about how can this happen? Yesterday I've tried to implement multiprocessing in Python script which is running on Spyder in Window PC. Here is the code I've first tried.
import multiprocessing
import time
start = time.perf_counter()
def do_something():
print('Sleeping 1 second...')
time.sleep(1)
print('Done sleeping')
p1 = multiprocessing.Process(target=do_something)
p2 = multiprocessing.Process(target=do_something)
p1.start()
p2.start()
p1.join()
p2.join()
finish = time.perf_counter()
print(f'Finished in {round(finish-start,2)} second(s)')
It's return an error.
AttributeError: Can't get attribute 'do_something' on <module '__main__' (built-in)
Then I search for survival from this problem and also my boss. And found this suggestion
Python's multiprocessing doesn't work in Spyder IDE
So I've followed it and installed Pycharm and try to run the code on PyCharm and it's seem to be work I didn't get AttributeError, however I got this new one instead of
RuntimeError:
An attempt has been made to start a new process before the
current process has finished its bootstrapping phase.
This probably means that you are not using fork to start your
child processes and you have forgotten to use the proper idiom
in the main module:
if __name__ == '__main__':
freeze_support()
...
The "freeze_support()" line can be omitted if the program
is not going to be frozen to produce an executable.
I've googled again then finally I got this
RuntimeError on windows trying python multiprocessing
what I have to do is adding this one line
if __name__ == '__main__':
before starting multiprocessing.
import multiprocessing
import time
start = time.perf_counter()
def do_something():
print('Sleeping 1 second...')
time.sleep(1)
print('Done sleeping')
if __name__ == '__main__':
p1 = multiprocessing.Process(target=do_something)
p2 = multiprocessing.Process(target=do_something)
p1.start()
p2.start()
p1.join()
p2.join()
finish = time.perf_counter()
print(f'Finished in {round(finish-start,2)} second(s)')
And it's work now moreover, it's not working only on PyCharm, now I can run this code on Spyder too. So that is why I have so curious? how come Spyder also work? This is quite persist because I'm also run this code on my other PC which is Window server 2016 with Spyder , I'm also do something.
Anyone can help explain what happen here why it's work?
Thank you.
There's a lot to unpack here, so I'll just give a brief overview. There's also some missing information like how you have spyder/pycharm configured, and what operating system you use, so I'll have to make some assumptions...
Based on the error messages you are probably using MacOS or Windows which means the default way python creates a child process is called spawn. This means it will start a completely new process from the python executable ("python.exe" on windows for example). It will then send a message to the new process telling it what function to execute (target), and optionally what arguments to call that function with. The new process will have to import the main file to have access to that function however, so if you are running the python interpreter in interactive mode, there is no "main" file to import, and you get the first error message: AttributeError.
The second error is also related to the importing of the "main" file. When you import a file, it basically just runs the file like any other python script. If you were to create a new child process during import that child would then also create a new child when it imports the same file. You would end up recursively creating infinite child processes until the computer crashed, so python disallows creating additional child processes during the import phase of a child process hence the RuntimeError.
I was working on a larger piece of code and I kept getting an error when the program just seemed to end without doing anything. I narrowed down the problem and reproduced it below. As far as I understand the code should print the sentence and it seems to work on other online IDE's while failing on mine. Feel like I'm missing something super simple.
Failing On: IDLE Python 3.8.3 32-bit from python.org
Works On: onlinegdb.com
Code:
import multiprocessing
def x():
print("This is x func")
if __name__ == '__main__':
multiprocessing.freeze_support()
p = multiprocessing.Process(target=x)
p.start()
p.join()
Output:
>>>
I think the issue is IDLE just doesn't output stuff from stuff outside the main process. Need to use consoles which would output everything from the main and all other processes. Reference : Python multiprocessing example not working
On my windows 10 machine (and seemingly other people's as well), Jupyter Notebook can't seem to handle some basic multiprocessing functions like pool.map(). I can't seem to figure out why this might be, even though a solution has been suggested to call the function to be mapped as a script from another file. My question, though is why does this not work? Is there a better way to do this kind of thing beyond saving in another file?
Note that the solution was suggested in a similar question here. But I'm left wondering why this bug occurs, and whether there is another easier fix. To show what goes wrong, I'm including below a very simple version that hangs on my computer where the same function runs with no problems when the built-in function map is used.
import multiprocessing as mp
# create a grid
iterable = [3, 5, 10]
def add_3(iterable):
a = iterable + 3
return a
# Below runs no problem
results = list(map(add_3, iterable))
print(results)
# multiprocessing attempt (hangs)
def main():
pool = mp.Pool(2)
results = pool.map(add_3, iterable)
return results
if __name__ == "__main__": #Required not to spawn deviant children
results = main()
Edit: I've just tried this in Spyder and I've managed to get it to work. Unsurprisingly running the following didn't work.
if __name__ == "__main__": #Required not to spawn deviant children
results = main()
print(results)
But running it as the following does work because map uses the yield command and isn't evaluated until called which gives the typical problem.
if __name__ == "__main__": #Required not to spawn deviant children
results = main()
print(results)
edit edit:
From what I've read on the issue, it turns out that the issue is largely because of the ipython shell that jupyter uses. I think there might be an issue setting name. Either way using spyder or a different ide solved the problem, as long as you're not still running the multiprocessing function in an iPython shell.
I faced a similar problem like this. I can't use multiprocessing with function on the same script. The solution that works is to put the function on different notebook file and import it use ipynb:
from ipynb.fs.full.script_name import function_name
pool = Pool()
result = pool.map(function_name,iterable_argument)
I have a PyQt5 GUI class that I want to be able to create multiple instances of either from an interactive console or normal run. I need these GUIs to be non-blocking so that they can be used while subsequent code runs.
I've tried calling app.exec__() in separate threads for each GUI like this answer, but the program sometimes crashes as the comment on the answer warned it would:
Run pyQT GUI main app in seperate Thread
And now I'm trying to get the code below working which I made based on this answer:
Run Pyqt GUI main app as a separate, non-blocking process
But when I run it the windows pop and and immediately disappear
import sys
from PyQt5 import QtWidgets, QtGui, QtCore
import time
class MainWindow(QtWidgets.QWidget):
def __init__(self):
# call super class constructor
super(MainWindow, self).__init__()
# build the objects one by one
layout = QtWidgets.QVBoxLayout(self)
self.pb_load = QtWidgets.QPushButton('Load')
self.pb_clear= QtWidgets.QPushButton('Clear')
self.edit = QtWidgets.QTextEdit()
layout.addWidget(self.edit)
layout.addWidget(self.pb_load)
layout.addWidget(self.pb_clear)
# connect the callbacks to the push-buttons
self.pb_load.clicked.connect(self.callback_pb_load)
self.pb_clear.clicked.connect(self.callback_pb_clear)
def callback_pb_load(self):
self.edit.append('hello world')
def callback_pb_clear(self):
self.edit.clear()
def show():
app = QtWidgets.QApplication.instance()
if not app:
app = QtWidgets.QApplication(sys.argv)
win = MainWindow()
win.show()
if __name__ == '__main__':
show()
show()
EDIT - I don't see how this question is a duplicate. The 'duplicate' questions are only slightly related and don't provide solutions to my problem at all.
I want to be able to create multiple instances of a GUI (MainWindow in my example) by calling the show() function from either an interactive session or script, and I want those windows to stay on my screen while subsequent code is running.
EDIT2 - When I run the code as a script I can do what I want by using multiprocessing, see this demo:
https://www.screencast.com/t/5WvJNVSLm9OR
However I still need help because I want it to also work in interactive Python console sessions, and multiprocessing does not work in that case.
It isn't necessary to use separate threads or processes for this. You just need a way to maintain a reference to each new window when importing the script in a python interactive session. A simple list can be used for this. It is only necessary to explictly start an event-loop when running the script from the command-line; in an interactive session, it will be handled automatically by PyQt.
Here is an implementation of this approach:
...
_cache = []
def show(title=''):
if QtWidgets.QApplication.instance() is None:
_cache.append(QtWidgets.QApplication(sys.argv))
win = MainWindow()
win.setWindowTitle(title)
win.setAttribute(QtCore.Qt.WA_DeleteOnClose)
win.destroyed.connect(lambda: _cache.remove(win))
_cache.append(win)
win.show()
if __name__ == '__main__':
show('Foo')
show('Bar')
sys.exit(QtWidgets.QApplication.instance().exec_())
This is a minor addendum to #ekhumoro's answer. I don't have enough reputation to only add a comment so I had to write this as an answer.
#ekhumoro's answer almost fully answers #Esostack's question, but doesn't work in the Ipython console. After many hours of searching for the answer to this question myself, I came across a comment from #titusjan in a three year old thread (here) also responding to a good answer from #ekhumoro.
The missing part to #ekhumoro's answer which results in the gui windows freezing for Ipython specifically is that Ipython should be set to use the qt gui at launch or once running.
To make this work with Ipython:
Launch Ipython with ipython --gui=qt5
In a running Ipython console run the magic command %gui qt5
To fix it from a Python script you can run this function
def fix_ipython():
from IPython import get_ipython
ipython = get_ipython()
if ipython is not None:
ipython.magic("gui qt5")