Ошибка с подпроцессом в скрипте python

Я создаю программу, где я буду конвертировать файлы с использованием subprocesses . Код, который я использую для преобразования:

 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. eg 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. Eg .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. eg 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. Eg .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. eg 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. Eg .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. eg 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. Eg .Jpeg: ") body, ext = os.path.splitext("filename") from subprocess import check_call check_call(["ffmpeg" ,"-i", filename , + body + Fileextension]) 

Когда я запускаю программу, я получаю ошибку:

• потоковые данные в команду с подпроцессом. Popen
• Как запустить файл в своей программе по умолчанию, а затем закрыть его, когда скрипт заканчивается?
• python subprocess set shell var. а затем запустить команду - как?
• Возвращаемое значение из подпроцесса Python
• Отключить вывод консоли из подпроцесса. Открыть в Python

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

Любые идеи относительно того, как я могу это решить. Код был бы очень признателен, но в этот момент любая помощь была бы высоко оценена.

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