Mypy switches to Python-compatible syntax

[Jukka Lehtosalo]

Hi All!

Mypy now has a Python-compatible syntax! The implementation is already self-hosting, but it should still be considered very experimental. This is a huge change which touched almost every source code file in the repository, and there are still many unfixed bugs.

Here is small example of the new syntax:

  import typing

  def fib(n: int) -> None:

      a, b = 0, 1

      while a < n:

          print(a)

          a, b = b, a+b

I have mostly updated the web site and documentation to reflect the new syntax. The Mypy Tutorial (formerly Mypy Overview) is largely rewritten:

http://www.mypy-lang.org/tutorial.html

The update also adds more content to the tutorial that isn't directly related to the syntax switch.

Since the mypy implementation is now a valid Python 3 program, there is no need for a translation step before running it. Thus also the old mypy-py repository is no longer needed to run mypy. Instead, mypy now uses the standard Python setup.py mechanism for installation. Have a look at the updated README for details:

https://github.com/JukkaL/mypy/blob/master/README.md

I have updated the example programs on the web site:

http://www.mypy-lang.org/examples.html

I also updated the mypy roadmap:

http://www.mypy-lang.org/roadmap.html

If you are thirsty for more code to look at, point your browser at the git repository:

https://github.com/JukkaL/mypy/tree/master/samples

https://github.com/JukkaL/mypy/tree/master/mypy

From now on, the old syntax is considered legacy and will not be supported by the implementation. There will be a tool for migrating mypy code written using the old syntax to the new syntax. The tool is already functional, but it still needs a bit if polish before it's generally useful. I will notify when it's available on this blog. I'll also write a longer blog post discussing the new syntax in more detail at a later date.

Any feedback is appreciated! The syntax is still work in progress, and improvements are possible.

Jukka