Error with subprocess in python script

I am creating a program where I will convert files using subprocesses. The code I am using for the conversion is:

import tornado.ioloop
import tornado.web
import os

print "If at any point you wish to quit the program hit Ctrl + C"

filetype = raw_input("What kind of file would you like to convert? Audio, Image, Video or Document: ")

if filetype == "Document":
    path = raw_input("Please drag and drop the directory in which the file is stored into the terminal:")
    os.chdir(path[1:-2])
    filename = raw_input("Please enter the name of the file you would like to convert, including the file-type. e.g. test.txt, however please do make sure that the file-name does not have any spaces:")
    Fileextension = raw_input("What filetype would you like the program to convert your file to. E.g. .txt: ")
    from subprocess import check_call   
    check_call(["unoconv " ,"-f ", Fileextension , + filename])

elif filetype == "Audio":
    path = raw_input("Please drag and drop the directory in which the file is stored into the terminal:")
    os.chdir(path[1:-2])
    filename = raw_input("Please enter the name of the file you would like to convert, including the file-type. e.g. test.txt, however please do make sure that the file-name does not have any spaces:")
    Fileextension = raw_input("What filetype would you like the program to convert your file to. E.g. .mp3: ")
    body, ext = os.path.splitext("filename")
    check_call(["ffmpeg" ,"-i", filename , + body + Fileextension])

elif filetype == "Video":
    path = raw_input("Please drag and drop the directory in which the file is stored into the terminal:")
    os.chdir(path[1:-2])
    filename = raw_input("Please enter the name of the file you would like to convert, including the file-type. e.g. test.txt, however please do make sure that the file-name does not have any spaces:")
    Fileextension = raw_input("What filetype would you like the program to convert your file to. E.g. .mp4: ")
    body, ext = os.path.splitext("filename")
    from subprocess import check_call   
    check_call(["ffmpeg" ,"-i", filename , + body + Fileextension])

elif filetype == "Image":
    path = raw_input("Please drag and drop the directory in which the file is stored into the terminal:")
    os.chdir(path[1:-2])
    filename = raw_input("Please enter the name of the file you would like to convert, including the file-type. e.g. test.txt, however please do make sure that the file-name does not have any spaces:")
    Fileextension = raw_input("What filetype would you like the program to convert your file to. E.g. .Jpeg: ")
    body, ext = os.path.splitext("filename")
    from subprocess import check_call   
    check_call(["ffmpeg" ,"-i", filename , + body + Fileextension])

When i run the program now I get the error:

  File "conversion.py", line 15, in <module>
    check_call(["unoconv " ,"-f ", Fileextension , + filename])
TypeError: bad operand type for unary +: 'str'

Any ideas as to how i can solve this. Code would be much appreciated, but at this point any help would be much appreciated.

As the error suggests you have both a , and + in the array. Based on the other things you're doing, you probably want to get rid of the , after Fileextension. You probably want to change all those lines to something like

subprocess.check_call(['unoconv', '-f', Fileextension, filename])

Note that I also got rid of the space in "unoconv " because it will otherwise be looking for that space as part of the executable name.

When passing a list to check_call each list element is treated as an argument to the process (which is the first list element). So if you want to run unoconv -f file.ext your list for check_call becomes a 3 element list: ['unoconv', '-f', '.txt', 'file.ext']

You seem to be mixing up the string concatenation to put the extension on the filenames and building the list of arguments.