C:\Users\Kevin\Desktop>type poll.py
track = input("Enter track name.")
artist = input("Enter artist name.")
print("Ok, adding track {} with artist {} to playlist.".format(track, artist))

C:\Users\Kevin\Desktop>type test.py
from subprocess import Popen, PIPE

def read_available(stdout):
    data = stdout.peek()
    stdout.read(len(data))
    return data

p = Popen(["python", "poll.py"], stdin=PIPE, stdout=PIPE)

inputs = [b'All Star\n', b'Smash Mouth\n']
outputs = []
outputs.append(read_available(p.stdout))
for x in inputs:
    p.stdin.write(x)
    p.stdin.flush()
    outputs.append(read_available(p.stdout))

print(outputs)

C:\Users\Kevin\Desktop>test.py
[b'Enter track name.', b'Enter artist name.', b'Ok, adding track All Star with artist Smash Mouth to playlist.\r\n']