In this example is the ".txt" supposed to be referenced as the type of file, so we should replace it with with png, PDF, etc.?

Answer 1

Correct. However, you may need special methods to read files other than plaintext.

Answer 2

We are not really sure which example you're talking about, since the Q&A does not link back to the lesson slides. Can you elaborate on your question? Is this about reading from text files?

Answer 3

For example in open("filename.txt"), the .txt part is referring to the extension of a file correct?

Answer 4

Yep. You can't just open a pdf as plaintext.

https://stackoverflow.com/questions/9951427