Problems using subprocess.call() in Python 2.7.2 on Windows

Question

I'm trying the following and its failing with an error. I've tried to run it from Python shell/from a script/ on the windows console by invoking python on console. Nothing seems to work. Always the same error.

from subprocess import call
>>>pat = "d:\info2.txt"

>>> call(["type",pat])

>>>Traceback (most recent call last):
  File "<pyshell#56>", line 1, in <module>
    call(["type",pat])
  File "C:\Python27\lib\subprocess.py", line 493, in call
    return Popen(*popenargs, **kwargs).wait()
  File "C:\Python27\lib\subprocess.py", line 679, in __init__
    errread, errwrite)
  File "C:\Python27\lib\subprocess.py", line 893, in _execute_child
    startupinfo)
WindowsError: [Error 2] The system cannot find the file specified

does anyone know what is wrong here.!!???

even the simple call(["date"]] without any arguements also fails with the same error.

I'm using : Python 2.72 32bit version on a windows 7 machine.

Answer 1

Add shell=True to call:

>>> import subprocess
>>> subprocess.call('dir', shell=True)
0

As you see, it gives as value the return code, not the output of dir. Also, it waits till the command completes, so doing

>>> subprocess.call('date', shell=True)

will wait for you to enter a new date.

edit: If you want to capture the output, use subprocess.check_output. The DOS command type for example prints out the contents of a file. So, suppose that your file info2.txt contains your username, you would do:

>>> import subprocess
>>> path = r'd:\info2.txt'
>>> output = subprocess.check_output(['type', path], shell=True)
>>> print output
Vinu

For all the ways to call external commands in Python, see this comprehensive overview to a related question, for more about subprocess specifically, see this article by Doug Hellmann.