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

问题:

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 "", line 1, in      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.

回答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.

回答2:

The 'type' command doesn't run because it's an internal command - internal to the command interpreter/shell called CMD.EXE. You have to call "cmd.exe type filename" instead. The exact code is:

call(['cmd','/C type abc.txt']) 

回答3:

pat = "d:\info2.txt" 

In Python and most other programming languages, \ is an escape character, which is not included in a string unless doubled. Either use a raw string or escape the escape character:

pat = "d:\\info2.txt" 

回答4:

Escape the \ with \\:

pat = "d:\\info2.txt" 

or use "raw" strings:

pat = r"d:\info2.txt" 

文章来源: Problems using subprocess.call() in Python 2.7.2 on Windows