In Python 3 you can iterate over the lines of standard input, the loop will stop when EOF is reached:
from sys import stdin
for line in stdin:
print(line, end='')
line
includes the trailing \n
character
Run this example online: https://ideone.com/rUXCIe
This might be what most people are looking for, however if you want to just read the whole input until EOF into a single variable (like OP), then you might want to look at this other answer.