Question

I noticed the following using Python 2.5.2 (does not occur using 2.7):

#!/usr/bin/python

import sys

for line in sys.stdin:
   print line,

Output:

$ echo -e "one\ntwo\nthree" | python test.py
$ one
$ two
$ three

as expected. However, if I import subprocess to the this script:

#!/usr/bin/python

import sys
import subprocess

for line in sys.stdin:
   print line,

Output:

$ echo -e "one\ntwo\nthree" | python test.py
$ two
$ three

What happened to the first line of output?

Update:

I think I may have discovered the root of the problem. I had a file named time.py in my cwd. A time.pyc is being created every time I run the script with subprocess imported, suggesting that ./time.py is also being imported. The script runs normally if I delete the .pyc and time.py files; however, there is still the question of why a subprocess import would cause ./time.py to be imported as well?

I have narrowed it down even further to the exact line in time.py that causes the strange behaviour. I have stripped down the working dir and file content to just that which affects the output:

test.py

#!/usr/bin/python

import sys
import subprocess

for line in sys.stdin:
   print line,

time.py

#!/usr/bin/python

import sys

for line in sys.stdin:
   hour = re.search(r'\b([0-9]{2}):', line).group(1)

Running test.py with any kind of input results in the first line of output being omitted and time.pyc being created.

Answer 1

Sounds like your local time.py will be imported instead of the global time module. You might want to rename it, or at least start checking if it was run as a script or imported as a module.

This will prove it for you if you want to test it.

#!/usr/bin/python

import sys

# Test that script was run directly
if __name__=='__main__':
    for line in sys.stdin:
       hour = re.search(r'\b([0-9]{2}):', line).group(1)
else:
    print 'Imported local time.py instead of global time module!'
    sys.exit(1)