The smallest pipeable python script

Python is a very capable scripting language, but when I was new to it, I felt that it was rather verbose, and hard to express things in a short way. I have subsequently learned that this is all about finding the name of the appropriate library, and a little bit about how to optimally use the syntactic sugars in python. 

Therefore, it turns out useful to gather a bunch of snippets, for reminding about how to go about certain typical task.

One such task, when working in a unix environment, is how to write text processing scripts that accept input on standard input, and writes the output on standard out, so that the script can easily  be chained together with other tools by the use of unix pipes.

The above is easily done in the following way, demonstrated below in its (almost) shortest possible syntax:

from sys import stdin, stdout
for line in stdin: