Develop Reference

Running Batch File from Python

I am trying to run a batch file through python; however, it is not recognizing the path. It stops reading the path after the space between 'Practice' and 'Folder'. How can I fix this? I've tried the r and using forward and backward slashes. Any help would be awesome. Thank you!
import os
Practice = r"C:\Users\Username\Desktop\Practice Folder\Practice.bat"
os.system(Practice)
'C:\Users\Username\Desktop\Practice' is not recognized as an internal
or external command, operable program or batch file.

Change working directory to the script directory as you are using some relative redirection paths. Pushd changes current directory to any drive and can map network drives. The && chains commands and only runs the right hand command if the left hand command succeeds. %UserProfile% is a standard environmental variable which is usually better then using a fixed path of C:\Users\Username.
import os
Practice = r'pushd "%UserProfile%\Desktop\Practice Folder" && Practice.bat'
os.system(Practice)

Try using call from subprocess module.
You need to enclose the command only in double quotes.
from subprocess import call
call(r'"C:\Users\Username\Desktop\Practice Folder\Practice.bat"')
(Notice the order of placing quotes...)
This would even work with os.system() provided you take care the order of quotation marks.
from os import system
system(r'"C:\Users\Username\Desktop\Practice Folder\Practice.bat"')
This should help fix your problem.

You probably need to use two types of quotation marks e.g.
import os
Practice = r"'C:\Users\Username\Desktop\Practice Folder\Practice.bat'"
os.system(Practice)
As it is, your string does not contain quotation marks - you need to include quotation marks within your string or else Windows will think that Folder\Practice.bat is an argument to the command rather than a continuation of the file path

Try this
import os
Practice = os.path.abspath(r"C:\Users\Username\Desktop\Practice Folder\Practice.bat")
Edit:
Something like this worked for me
os.system(r'"C:\Users\Username\Desktop\Practice Folder\Practice.bat"')

python: How does subprocess.check_output create it's calls?

I'm trying to read the duration of video files using mediainfo. This shell command works
mediainfo --Inform="Video;%Duration/String3%" file
and produces an output like
00:00:33.600
But when I try to run it in python with this line
subprocess.check_output(['mediainfo', '--Inform="Video;%Duration/String3%"', file])
the whole --Inform thing is ignored and I get the full mediainfo output instead.
Is there a way to see the command constructed by subprocess to see what's wrong?
Or can anybody just tell what's wrong?

Try:
subprocess.check_output(['mediainfo', '--Inform=Video;%Duration/String3%', file])
The " in your python string are likely passed on to mediainfo, which can't parse them and will ignore the option.
These kind of problems are often caused by shell commands requiring/swallowing various special characters. Quotes such as " are often removed by bash due to shell magic. In contrast, python does not require them for magic, and will thus replicate them the way you used them. Why would you use them if you wouldn't need them? (Well, d'uh, because bash makes you believe you need them).
For example, in bash I can do
$ dd of="foobar"
and it will write to a file named foobar, swallowing the quotes.
In python, if I do
subprocess.check_output(["dd", 'of="barfoo"', 'if=foobar'])
it will write to a file named "barfoo", keeping the quotes.

Maya ignores my doubles quotations

I'm having troubles starting maya from a python script with a mel command. Or rather I have a problem getting the mel command to run, maya launches just fine.
This is what the maya documentation says about starting with a mel command:
-command [mel command]
Runs the specified command on startup. The command should be enclosed
in double quotes to protect any special characters, including spaces.
Whatever I try Maya just ignores my doublequotes and gives me a syntax error.
This is my code:
import os
dir = "D:\exampleProject\maya"
os.system('maya.exe -command \"setProject \"'+dir+'\"\"')
I figure this would be read as this in maya: setProject "D:\exampleProject\maya" (which is what I want)
What I get is instead: setProject D:\exampleProject\maya which generates a syntax error in maya due to the lack of "" around the directory path.

Answer from comments
From the MEL documentation, it states that "Every statement in MEL must end with a semi-colon (;)."
MEL strings also require quotations to be escaped, therefore double escape the internal quotations.
'maya.exe -command \"setProject \\\"'+dir+'\\\";\"'

If all you need is to set the project you can use the startup flag "-proj"
maya.exe the/scene/iwant/to/open.ma -proj the/project/root
See the Documentation

Dropping a file onto a python script in windows - avoid Windows use of backslashes in the argument

I know all about how Windows uses backslashes for filenames, etc., and Unix uses forward. However, I never use backslashes with strings I create in my code. However:
When windows explorer "drops" a file onto a python script, the string it passes contains backslashes. These translate into escape sequences in the strings in the sys.argv list and then I have no way to change them after that (open to suggestions there)
Is there any way I can somehow make windows pass a literal string or ... any other way I can solve this problem?
I'd love my script to be droppable, but the only thing preventing me is windows backslashes.
EDIT:
Sorry everyone, the error was actually not the passing of the string - as someone has pointed out below, but this could still help someone else:
Make sure you use absolute path names because when the Windows shell will NOT run the script in the current directory as you would from a command line. This causes permission denied errors when attempting to write to single-part path-names that aren't absolute.

Cannot reproduce. This:
import os, sys
print sys.argv
print map(os.path.exists, sys.argv)
raw_input()
gives me this:
['D:\\workspaces\\generic\\SO_Python\\9266551.py', 'D:\\workspaces\\generic\\SO_Python\\9254991.py']
[True, True]
after dropping the second file onto the first one. Python 2.7.2 (on Windows). Can you try this code out?

Passing a multi-line string as an argument to a script in Windows

I have a simple python script like so:
import sys
lines = sys.argv[1]
for line in lines.splitlines():
print line
I want to call it from the command line (or a .bat file) but the first argument may (and probably will) be a string with multiple lines in it. How does one do this?
Of course, this works:
import sys
lines = """This is a string
It has multiple lines
there are three total"""
for line in lines.splitlines():
print line
But I need to be able to process an argument line-by-line.
EDIT: This is probably more of a Windows command-line problem than a Python problem.
EDIT 2: Thanks for all of the good suggestions. It doesn't look like it's possible. I can't use another shell because I'm actually trying to invoke the script from another program which seems to use the Windows command-line behind the scenes.

I know this thread is pretty old, but I came across it while trying to solve a similar problem, and others might as well, so let me show you how I solved it.
This works at least on Windows XP Pro, with Zack's code in a file called
"C:\Scratch\test.py":
C:\Scratch>test.py "This is a string"^
More?
More? "It has multiple lines"^
More?
More? "There are three total"
This is a string
It has multiple lines
There are three total
C:\Scratch>
This is a little more readable than Romulo's solution above.

Just enclose the argument in quotes:
$ python args.py "This is a string
> It has multiple lines
> there are three total"
This is a string
It has multiple lines
there are three total

The following might work:
C:\> python something.py "This is a string^
More?
More? It has multiple lines^
More?
More? There are three total"

This is the only thing which worked for me:
C:\> python a.py This" "is" "a" "string^
More?
More? It" "has" "multiple" "lines^
More?
More? There" "are" "three" "total
For me Johannes' solution invokes the python interpreter at the end of the first line, so I don't have the chance to pass additional lines.
But you said you are calling the python script from another process, not from the command line. Then why don't you use dbr' solution? This worked for me as a Ruby script:
puts `python a.py "This is a string\nIt has multiple lines\nThere are three total"`
And in what language are you writing the program which calls the python script? The issue you have is with argument passing, not with the windows shell, not with Python...
Finally, as mattkemp said, I also suggest you use the standard input to read your multi-line argument, avoiding command line magic.

Not sure about the Windows command-line, but would the following work?
> python myscript.py "This is a string\nIt has multiple lines\there are three total"
..or..
> python myscript.py "This is a string\
It has [...]\
there are [...]"
If not, I would suggest installing Cygwin and using a sane shell!

Have you tried setting you multiline text as a variable and then passing the expansion of that into your script. For example:
set Text="This is a string
It has multiple lines
there are three total"
python args.py %Text%
Alternatively, instead of reading an argument you could read from standard in.
import sys
for line in iter(sys.stdin.readline, ''):
print line
On Linux you would pipe the multiline text to the standard input of args.py.
$ <command-that-produces-text> | python args.py