I'm working with a large existing Python codebase and would like to start adding in type annotations so I can get some level of static checking. I'm imagining something like Erlang, Strongtalk, or Typed Scheme/Racket.
I've seen quick-and-dirty decorators that insert dynamic checks based on function parameter and return type annotations, but I'm looking for something that is more robust and that performs checks at compile-time.
What tools are available right now for this kind of thing? I'm familiar with compilers and type checking and am definitely willing to improve an incomplete tool if it has a good foundation.
(Note: I'm not interested in a discussion of the pros/cons of static typing.)
EDIT: An example:
def put(d, k, v): d[k] = v
I'd like to be able to annotate the put
function as having type put<K,V>(dict<K,V>, K, V) -> None
.
UPDATE: The new PEP 484 (Sep 2014) defines a standard for static typing and type annotations in Python 3.5+. There's a type-checking tool called mypy that is compatible with PEP 484.
Edit 2016-11-11: Just use mypy. Type hints can be added gradually. In Python 3 source code, it verifies standard PEP 484 type hints. Types can still be expressed in Python 2 using special comments. Guido likes it.
This post was originally written a long time ago before mypy was a thing. I've preserved the post's original content below, even though it isn't quite accurate.
Original post:
You might want to check out some of the projects mentioned in this related StackOverflow post on static analysis for Python.
In summary:
Since Python uses duck typing extensively, things that might be called "type errors" in other languages might end up being "object X doesn't support method Y" in Python.
Edit 2011-05-17:
I agree with delnan that static typing is not possible for Python [apparently wrong]. But since our skepticism doesn't seem to deter you, I can only give you more information on the subject. I present:
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