python subprocess updates its lines (\r) - i need every update

Question

As suggested in an answer to my question "Python: start terminal program and parse its output while it's running" i am using a subprocess construct to communicate with a program:

server = subprocess.Popen(["meteor", "--port",  port], stdout=subprocess.PIPE)

for line in iter(server.stdout.readline, ""):
  # Do something for example
  print(line)

The problem is: The subprocess (server) does not end each line with a newline directly as it is putting a (x2) at the end of a line, when the message duplicates.

But i want to react on every line update. So I want to handle \r like \n and not just iterate over finished lines, i want to iterate over the available string until the next "pause" wether it is a \r or \n or another line break to get the information directly when it appears, not only when the server sends a \n. How can i do that?

Answer 1

maybe if you tried to use a non-blocking pipe connection. then read the stream much like a socket connection (in a while(true) loop)...hopefully this'll point you in the right direction.

from fcntl import fcntl, F_GETFL, F_SETFL
from os import O_NONBLOCK, read

server = subprocess.Popen(["meteor", "--port",  port], stdout=subprocess.PIPE)
flags = fcntl(server.stdout, F_GETFL) # get current p.stdout flags
fcntl(server.stdout, F_SETFL, flags | O_NONBLOCK)

while True:
    print read(server.stdout.fileno(), 1024),

you'll need to add error handling for a dropped connection or no more data.