ndb Key Snippet is Incorrect

[howinator]

In which file did you encounter the issue?

appengine/standard/ndb/entities/snippets.py

Did you change the file? If so, how?

I have a fix which properly describes that keys are an instance property and not a class property. You can see this change here.

Describe the issue

I may have already properly described the issue, but the snipped in one of the ndb snippets indicates that the key property is a class attribute. It is actually an instance attribute. My branch above fixes this and I can submit a PR once I get the 👍 on this issue.

[theacodes]

Thanks, @howinator, would you be interested in sending a pull request to fix this?

[howinator]

Of course, @jonparrott. PR opened as #1150 😄