Question or problem about Python programming:
I have a Python script that needs to execute an external program, but for some reason fails.
If I have the following script:
import os; os.system("C:\\Temp\\a b c\\Notepad.exe"); raw_input();
Then it fails with the following error:
If I escape the program with quotes:
import os; os.system('"C:\\Temp\\a b c\\Notepad.exe"'); raw_input();
Then it works. However, if I add a parameter, it stops working again:
import os; os.system('"C:\\Temp\\a b c\\Notepad.exe" "C:\\test.txt"'); raw_input();
What is the right way to execute a program and wait for it to complete? I do not need to read output from it, as it is a visual program that does a job and then just exits, but I need to wait for it to complete.
Also note, moving the program to a non-spaced path is not an option either.
This does not work either:
import os; os.system("'C:\\Temp\\a b c\\Notepad.exe'"); raw_input();
Note the swapped single/double quotes.
With or without a parameter to Notepad here, it fails with the error message
How to solve the problem:
subprocess.call will avoid problems with having to deal with quoting conventions of various shells. It accepts a list, rather than a string, so arguments are more easily delimited. i.e.
import subprocess subprocess.call(['C:\\Temp\\a b c\\Notepad.exe', 'C:\\test.txt'])
Here’s a different way of doing it.
If you’re using Windows the following acts like double-clicking the file in Explorer, or giving the file name as an argument to the DOS “start” command: the file is opened with whatever application (if any) its extension is associated with.
filepath = 'textfile.txt' import os os.startfile(filepath)
import os os.startfile('textfile.txt')
This will open textfile.txt with Notepad if Notepad is associated with .txt files.
The outermost quotes are consumed by Python itself, and the Windows shell doesn’t see it. As mentioned above, Windows only understands double-quotes.
Python will convert forward-slashed to backslashes on Windows, so you can use
os.system('"C://Temp/a b c/Notepad.exe"')
The ‘ is consumed by Python, which then passes “C://Temp/a b c/Notepad.exe” (as a Windows path, no double-backslashes needed) to CMD.EXE
At least in Windows 7 and Python 3.1,
os.system in Windows wants the command line double-quoted if there are spaces in path to the command. For example:
TheCommand = '\"\"C:\\Temp\\a b c\\Notepad.exe\"\"' os.system(TheCommand)
A real-world example that was stumping me was cloning a drive in VirtualBox. The
subprocess.call solution above didn’t work because of some access rights issue, but when I double-quoted the command,
os.system became happy:
TheCommand = '\"\"C:\\Program Files\\Sun\\VirtualBox\\VBoxManage.exe\" ' \ + ' clonehd \"' + OrigFile + '\" \"' + NewFile + '\"\"' os.system(TheCommand)
import win32api # if active state python is installed or install pywin32 package seperately try: win32api.WinExec('NOTEPAD.exe') # Works seamlessly except: pass