Do not overwrite a file that is used later

[bkmgit]

Make a copy of the file.

[gcapes]

Thanks for the PR.
This is a callout showing what not to do. So I'm afraid that changing the example to a better practice negates the point of the callout.

[emcaulay]

This edit to the episode 4 addresses a concern raised and discussed in issue #1375 . I recommend accepted and merging these changes in.

I just realized this PR is already closed, so my comment here is after the fact!

[emcaulay]

Now, I'm seeing that this PR was not accepted, but I do think it is a good revision and addresses the concern discussed in #1375. I think it seems a little cruel to set up a learner to destroy a file by mistake when we expect them to have the intact file for continuing the lesson.