Read Python stdin from pipe, without blocking on empty input

Question

I am trying to read stdin in a Python script, while receiving from pipe.

I used these lines:

for line in sys.stdin:
    print line

And run the script: echo "test" | script.py

So far it works fine. However if I don't use a pipe the program sticks at the for command. Meaning that calling: ./script.py will make the script not work. How can I fix this?

Answer 1

Edit: you apparently don't even want it to read lines in this case or handle KeyboardInterrupt, so what you need to do is check for empty stdin. Check if you are a terminal and pass as shown in the edited example.

---

sys.stdin is file-like. Try:

if not sys.stdin.isatty():
    data = sys.stdin.readlines()
    # Do something with data

If you run this with no stdin I don't think it will hang like it did for you before... because sys.stdin will be empty. The function should then continue.

Answer 2

You can check if the program has been piped by calling isatty on the file descriptor derived from sys.stdin.

Like so :

import os
import sys

if not os.isatty(sys.stdin.fileno()):
    print (sys.stdin.readlines())
else:
    print ("Skip, so it doesn't hang")

Example 1 :

 echo "test" | python ./script.py
 ['test\n']

Example 2 :

 python ./script.py 
 Skip, so it doesn't hang