Use io.open in notebookapp.py to fix #4303

[slel]

Following the discussion at #4340, in Python 2 we need io.open
rather than open if using a file descriptor rather than a file name.

[takluyver]

Can you add encoding='utf-8' here? It's not the same problem, but it would be good to do it while we're looking at this code.

[takluyver]

The test failures are because of tornado 6.0a1. I've committed to 5.7.x to limit it to tornado 5.x; I'll close and reopen this pull request to test it again.

[takluyver]

Sorry, I think I told you to change the wrong one. This one needs to stay as regular open(), because the JSON module on Python 2 produces bytes, not unicode.

I thought we were looking at this line, but it already uses io.open():

notebook/notebook/notebookapp.py

Line 1699 in 0579bc0

with io.open(self.browser_open_file, 'w', encoding='utf-8') as f:

[slel]

If commit f8d7d40 has all that is needed, can you use only that commit
and leave out the further two commits in this branch when you merge?

[takluyver]

Yup. I'll open a new PR so it re-runs the CI tests with just that.

[takluyver]

See #4349

[slel]

Grepping for with open and with io.open in the 5.7.x branch
gives about 30 of each... it might make sense to go through them
systematically and check whether more open should become io.open
and whether more encoding='utf-8' should be added.

$ grep -r "with open" .
$ grep -r "with io.open" .

$ grep -r "with open" . | wc -l
$ grep -r "with io.open" . | wc -l

[takluyver]

Merged #4349