Return types for some ensure functions

[bgyori]

For functions like ensure_open_zip, the return value is documented as

:yields: An open file object

so I thought this wold be something I can call e.g., read() on. Checking the type of the returned value, it's contextlib._GeneratorContextManager and it took me a little while to figure out that this means I have to use with to interact with this function. Is the documentation and type annotation for these functions correct?