Images not indexable

[RLPfeiffer]

A new list for fileNamesList is instantiated with the other variables. The following line is added to the openImages function to populate the list:
self.fileNameList.append(fileName)

However, when I try and call from that list to return images I get these errors: File "ImageViewer.py", line 97, in chooseGrayscaleImage
self.chooseDisplayImage(self.fileNameList[index])
File "ImageViewer.py", line 91, in chooseDisplayImage
pixmap = QPixmap.fromImage(self.rawImages[index])
TypeError: list indices must be integers or slices, not str