[Tutor] Regarding "IDLE Subprocess Didn't Make Connection" Error

[Avi Gross]

I was wondering if I was the only one who felt the urge to apply a tad of humor and suppressed most of the thoughts about idol/IDLE worship and other puns so I am glad to see Steve do just a little of the same.

It seems that despite how portable Python is touted to be, quite a few people report problems in getting the basics working when installing. And if you can't get started, that is obviously a barrier. My suggestion earlier was based on the fact that IDLE is an add-on and they should first check if Python itself works. Any text editor can be used that just produces plain text and scripts can be run in other ways.

But I have a thought. An old an often effective method to solve a problem is to search in the source code. Yes, you did not write IDLE. 

 I am still not clear on how IDLE aborts on startup but I recall that IDLE may be written in Python with source code available. I went into python to see where to look by seeing the path it would search.

>>> import sys
>>> print(sys.path)

I then followed a trail and what I found was idlelib with many components and when I import that library in the IDLE main unit I see some of the results:

>>> import idlelib
>>> dir(idlelib)
['__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__path__', '__spec__', 'autocomplete', 'autocomplete_w', 'calltip_w', 'calltips', 'config', 'debugger', 'debugger_r', 'debugobj', 'debugobj_r', 'hyperparser', 'iomenu', 'macosx', 'multicall', 'pyparse', 'rpc', 'run', 'scrolledlist', 'stackviewer', 'testing', 'tree', 'windows', 'zoomheight']

I could potentially follow along, and for a while I did. I think that after a few steps, on my machine, it hits pyshell in C:\Users\avid2016\AppData\Local\Programs\Python\Python37-32\Lib\idlelib and then runs code starting with:

#! /usr/bin/env python3

import sys

try:
    from tkinter import *
except ImportError:
    print("** IDLE can't import Tkinter.\n"
          "Your Python may not be configured for Tk. **", file=sys.__stderr__)
    raise SystemExit(1)

And it goes on and on. It imports all kinds of things and creates many classes and if called directly, runs a big function called main. I searched for "subprocess" and "IDLE" to see if the file had whatever error message you saw and I think I found it in the definition of a function:

    def display_no_subprocess_error(self):
        tkMessageBox.showerror(
            "Subprocess Startup Error",
            "IDLE's subprocess didn't make connection.  Either IDLE can't "
            "start a subprocess or personal firewall software is blocking "
            "the connection.",
            parent=self.tkconsole.text)

Correction, the first argument of "self' was a hint and that is actually a method in: 
class ModifiedInterpreter(InteractiveInterpreter):

Now if that is the error message, you work backwards to see when it might have been called/triggered.

Searching for a call to that method shows two places:

Here is one snippet:

self.spawn_subprocess()
        #time.sleep(20) # test to simulate GUI not accepting connection
        # Accept the connection from the Python execution server
        self.rpcclt.listening_sock.settimeout(10)
        try:
            self.rpcclt.accept()
        except socket.timeout:
            self.display_no_subprocess_error()
            return None

Here is the other:

self.spawn_subprocess()
        try:
            self.rpcclt.accept()
        except socket.timeout:
            self.display_no_subprocess_error()
            return None

I am going to stop now and suggest it happens when IDLE creates a subprocess to run in parallel and plays games with sockets and fails.


FWIW, the method called before is:

    def spawn_subprocess(self):
        if self.subprocess_arglist is None:
            self.subprocess_arglist = self.build_subprocess_arglist()
        self.rpcsubproc = subprocess.Popen(self.subprocess_arglist)

Presumably something goes wrong in there but I suspect the Popen failed.

Why would it fail? Well, it could be many things including whatever actual info is in the arglist ...

That might take plenty of additional digging including suggestions about something not being set right in the path or other registry components or some rogue library component being imported rather than the intended one or so much more. But, in theory, you can even take the source code and run it more carefully and debug this. Not something for a novice.

Not sure if that helps but if I actually had to read all that code and do serious debugging, it might take me days and I have a funeral and a party (unrelated) to go to today alone 😉


-----Original Message-----
From: Tutor <tutor-bounces+avigross=verizon.net at python.org> On Behalf Of Steven D'Aprano
Sent: Saturday, November 17, 2018 6:18 AM
To: tutor at python.org
Subject: Re: [Tutor] Regarding "IDLE Subprocess Didn't Make Connection" Error

On Thu, Nov 15, 2018 at 03:38:28PM -0800, Break fast wrote:

> "IDLE subprocess didn't make connection. Either IDLE can't start a 
> subprocess, or personal Firewall software is blocking the connection"
> 
> I have been researching this issue nonstop the last two days,

Without pausing to eat or sleep? You're more dedicated than I would be...


> and haven't had any luck in resolving the issue.

This is a common issue, there's probably a bazillion places that talk 
about it:

https://duckduckgo.com/?q=IDLE+subprocess+didn%27t+make+connection

Unfortunately there are many different things which could cause it (the 
error message is, frankly, unhelpful). This bug report looks promising:

https://bugs.python.org/issue14576

Try making sure that the HOME environment variable exists, and is 
writable.

 
> I am running Windows 7 (x64), and have installed Python 3.7.1 and 3.6.7
> numerous times now.

Why? Reinstalling should be the *last* resort, not first, and especially 
not reinstalling over and over and over again.



-- 
Steve
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