[Python] Why is stdout PIPE readline() not waiting for a newline character?

Why is print(line) in read_stdout printing every character instead of the entire line? I am expecting it to add to the queue once the newline character is reached, but it's just putting every character in the queue instead.

plugin_test.py:

from subprocess import PIPE, Popen
from threading import Thread
from queue import Queue, Empty
import re
import os
import sys

def read_stdout(stdout, data_q):
for line in stdout.readline():
print(line)
data_q.put(line)
stdout.close()

class Plugin():
name = ''

def __init__(self, **kwargs) -> None:
self.process = None

def run(self) -> bool:
try:
self.process = Popen(
[sys.executable, 'test.py'],
stdin=PIPE,
stdout=PIPE,
text=True)
except Exception as exc:
print("Could not create plugin process {}. {}".format(self.name, exc))
return False

self.data_q = Queue()
self.read_t = Thread(target=read_stdout, args=(self.process.stdout, self.data_q))
self.read_t.daemon = True
self.read_t.start()

try:
startup = self.data_q.get(timeout=10)
except Empty:
print("Plugin took to long to load {}.".format(self.name))
self.stop()
return False
else:
if 'Error' in startup:
print("Could not load plugin {}. {}".format(self.name, startup))
self.stop()
return False
elif '100%' in startup:
print("Plugin \"{}\" started.".format(self.name))

return True

def write(self, data : str) -> None:
self.process.stdin.write(data)
self.process.stdin.flush()

def read(self) -> str:
try:
data = self.data_q.get()
print("Got data ::{}::".format(data))
except Exception as exc:
print("Error reading data from plugin '{}'".format(exc))

def stop(self):
self.process.terminate()
self.process.wait()


if __name__ == '__main__':
plugin = Plugin()
plugin.run()


test.py:

print("this is a test")
print("this is a test2")
print("100%")


root@osboxes# python plugin_test.py

t
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