Get type information from isinstance assertions

[ddfisher]

Fixes #475.

Should probably be reviewed by someone who understands the checker's self.binder.

[gvanrossum]

LGTM, you an merge it yourself once the tests pass. Yay!

[gvanrossum]

Hold on, I don't know the binder that well.

--Guido (mobile)
On Apr 7, 2016 5:35 PM, "David Fisher" [email protected] wrote:

Fixes #475 #475.

Should probably be reviewed by someone who understands the checker's

self.binder.

You can view, comment on, or merge this pull request online at:

#1346
Commit Summary

• Get type information from isinstance assertions

File Changes

• M mypy/checker.py
  https://github.com/python/mypy/pull/1346/files#diff-0 (10)

Patch Links:

• https://github.com/python/mypy/pull/1346.patch
• https://github.com/python/mypy/pull/1346.diff

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#1346

[ddfisher]

One caveat that I realized is that this will widen the type if you assert something very defensively. For example:

def f(x: int):
  assert isinstance(x, object)
  # x now has type object
  return x + 1  # error

I ran this against our current annotations and found one instance of something like this. (Worked fine otherwise, though!)

[gvanrossum]

And what does the equivalent code using `if isinstance(x, object)` do?

[ddfisher]

Just checked -- it has the same behavior. (Which make sense, as I based this code on the if isinstance(...) code.)