Pydev showing 'undefined variable' for Jython code analysis - eclipse

Question

I have used Eclipse, Jython & Pydev for a long time. Upgrading as and when new releases arrived. All has worked very well until recently when the Pydev code completion started marking common items such as dir or print as 'undefined variable'. But the program ran correctly.
The error log showed:
'The python client still hasn't connected back to the eclipse java vm (will retry..)'
'Attempt: 2 of 5 failed, trying again...(socket connected still null)'
and more attempts to 5 out of 5
'Error connecting to python process(most likely cause for failure is firewall blocking...misconfigured network)'
Also, attempting to create a live jython console CTRL+ALT+ENTER gives the following error:
'Create interactive Console' has encountered a problem
Error initializing console.
Unexpected error connecting to console.
Failed to receive suitable Hello response from pydevconsole. Last msg received: Console already exited with value: 1 while waiting for an answer.
I have spent a lot of time looking for answers here and elsewhere that have included suggestions to check:
Mixed 32/64 bit installs; Firewall problems; IPV4 preference; localhost entries; path issues and others: all I've checked out with no success so far.
Software is Windows 10, Eclipse 4.21.0, Pydev 9.1.0.2021, Java JDK 11.0.13, Jython 2.7.2
I should be most grateful for any further help on this problem.
Many thanks

Answer 1

Well, you get that message because PyDev does spawn a shell and communicate with it for collecting code-completion results and the same happens for the interactive console.
Now, in both cases it seems like the socket communication is being prevented in your use case (as the messages states, the usual culprit is some firewall -- or possibly an anti-virus -- or some network misconfiguration).
Unfortunately, it's really hard for me to diagnose this as it's pretty much machine-dependent (all I can say is that I checked things here and Jython is working well, so, the issue lies in some misconfiguration on your machine).
I actually have plans to stop requiring that socket communication (for getting the completions from a shell) and using stdin/stdout (https://www.brainwy.com/tracker/PyDev/1183), but this still isn't done.
As Jython does run for you, you can try to create a simple server to verify a connection works.
i.e.: Create an echo_server.py with:
import socket
if __name__ == '__main__':
HOST = '127.0.0.1'
PORT = 65432
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
s.listen(1)
conn, addr = s.accept()
print('Connected by', addr)
data = conn.recv(1024)
conn.sendall(data)
print('Echo server finished')
and a client.py with:
import socket
if __name__ == '__main__':
HOST = '127.0.0.1'
PORT = 65432
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
s.sendall(b'Hello, world')
data = s.recv(1024)
print('Received %r' % (data,))
Then run the server part and then the client part and check if that does work properly for you.