Mypy: Question: Is the a project to automatically annotate functions?

[MartinThoma]

I am aware of MonkeyType, but as far as I know they are "only" using unit tests to infer types. This means if there are no unit tests for a piece of code, MonkeyType cannot help.

But sometimes you can still guess the type from the structure. I've added examples below.

How would such a "type guessing" tool be used?

1. One has a code base without type annotations and possibly with no or few tests
2. The type guesser is run and annotates the code in a way so that mypy would not complain about it.
3. The annotations are reviewed as the type guessing cannot be perfect

Is there something like that? Possibly a machine learning project which takes annotated code as input and builds a model to represent which variable names/methods typically represent which classes.

Example 1: Guess by usage within known functions

def a(b):
    c, d = 0, 1
    for _ in range(b):
        c, d = d, c+d
    return c

Even if you don't know what the code is doing, it is very reasonable to assume that b is an integer as it is used as an argument to range.

Example 2: Guess by method usage

def a(b):
    return b.split('.')[-1]

It is likely that b is a string, although a lot more is possible

Example 3: Guess by name

Some parameter names also give clear indicators:

• config => Dict[str, Any]
• index => int
• date => date or datetime
• y => float or int
  ...

[gvanrossum]

Thanks for asking! There's an experimental mypy feature, mypy suggest, that can do this (under limited circumstances).

If you need more help I recommend Gitter.

[gvanrossum]

I'm sorry, there are other tools that do this too. In particular pytype implements your "example 2" and make-stub-files can do (3).

[MartinThoma]

Thank you so much! I will have a look at all of them :-) (And thank you for developing / steering Python for so many years!)

[JelleZijlstra]

Also, MonkeyType doesn't use exclusively unit tests—it can also be used at runtime (at some performance cost) to gather type information.