Investigate the use of type hints

[drvinceknight]

See discussion on #454.

[marcharper]

It's Python 3 only, there are third party libraries like mypy that have some degree of Python 2 support (with a preprocessor that strips the type annotations I believe).

[marcharper]

Closing, we can reopen in the future if we drop python 2 support.

[marcharper]

In Python 3.6 there will supposedly be a way to do this in comments that is compatible with Python 2.7 and 3.6. So we could do this if we drop support for 3.x for x < 6 once 3.6 is released.

Alternatively we could drop support for Python 2.7 and "do it the right way". That's my preference. With the popularity of anaconda I'm skeptical that there is a real need to continue supporting Python 2. We could also get rid of the warnings in #476.

[drvinceknight]

In Python 3.6 there will supposedly be a way to do this in comments that is compatible with Python 2.7 and 3.6. So we could do this if we drop support for 3.x for x < 6 once 3.6 is released.

Perhaps we could wait for 3.7 so we still have the last two 3s?

What advantages do type hints give us? (I don't know what they are. If an explanation is too complicated I'll look it up :) Just being lazy.) I understand that it's about performance, would we need to go back and annotate a bunch of code?

Alternatively we could drop support for Python 2.7 and "do it the right way". That's my preference. With the popularity of anaconda I'm skeptical that there is a real need to continue supporting Python 2. We could also get rid of the warnings in #476.

I think it's still too early to drop py2...

Slightly related: https://python3statement.github.io/ Could be nice to include us on there?

[marcharper]

Type hints just indicate what the types of variables are for function arguments and return variables, and they can be explicit, like int or more vague, such as sequence. They actually don't do anything now other than providing a way to test the types, but they can (arguably) increase readability. It's possible that the interpreter could take advantage of the type hints eventually but right now I don't believe that cpython does anything other than parse the hints and make them available through the typing module.

[drvinceknight]

Cool, so we wouldn't have to go back and annotate but we could?

[marcharper]

Exactly.

[meatballs]

We could use the annotations instead of numpy style docstrings. There's a sphinx extension that will render the docs from them.

[meatballs]

Here's the extension: https://pypi.python.org/pypi/sphinx-autodoc-annotation/1.0

[marcharper]

Closing re: #808