Example error

http://www.khanacademy.org/api/v1/topic/tension-tutorial
http://www.khanacademy.org/api/v1/videos/the-force-of-tension
Downloading physics/3-Forces and Newton's laws of motion/6-Tension/1-The force of tension.mp4
http://www.khanacademy.org/api/v1/videos/mild-and-medium-tension
Downloading physics/3-Forces and Newton's laws of motion/6-Tension/2-Mild and medium tension.mp4
http://www.khanacademy.org/api/v1/videos/super-hot-tension
Downloading physics/3-Forces and Newton's laws of motion/6-Tension/3-Super hot tension.mp4
http://www.khanacademy.org/api/v1/videos/introduction-to-tension
Downloading physics/3-Forces and Newton's laws of motion/6-Tension/4-Introduction to tension.mp4
http://www.khanacademy.org/api/v1/videos/tension-part-2
Downloading physics/3-Forces and Newton's laws of motion/6-Tension/5-Introduction to tension (part 2).mp4
http://www.khanacademy.org/api/v1/videos/tension-in-an-accelerating-system-and-pie-in-the-face
Downloading physics/3-Forces and Newton's laws of motion/6-Tension/6-Tension in an accelerating system and pie in the face.mp4
http://www.khanacademy.org/api/v1/topic/treating-systems
http://www.khanacademy.org/api/v1/videos/treating-systems-the-hard-way
Downloading physics/3-Forces and Newton's laws of motion/7-Treating systems /1-Treating systems (the hard way).mp4
Traceback (most recent call last):
  File "app.py", line 84, in <module>
    main()
  File "app.py", line 81, in main
    k.visitCourse(k.parseCommandLineArguments())
  File "app.py", line 33, in visitCourse
    self.visitElement(requests.get(self._topicUrl + topic).json())
  File "app.py", line 38, in visitElement
    self.visitTopic(element)
  File "app.py", line 59, in visitTopic
    self.visitElement(requests.get(url).json())
  File "app.py", line 38, in visitElement
    self.visitTopic(element)
  File "app.py", line 59, in visitTopic
    self.visitElement(requests.get(url).json())
  File "app.py", line 38, in visitElement
    self.visitTopic(element)
  File "app.py", line 59, in visitTopic
    self.visitElement(requests.get(url).json())
  File "app.py", line 40, in visitElement
    self.visitVideo(element)
  File "app.py", line 68, in visitVideo
    self.saveFile(fileRequest, fileName)
  File "app.py", line 75, in saveFile
    with open(fileName, 'wb') as fileDescriptor:
FileNotFoundError: [Errno 2] No such file or directory: "physics/3-Forces and Newton's laws of motion/7-Treating systems /1-Treating systems (the hard way).mp4"