Update type annotation for create_model function

[uriyyo]

Update type annotation for create_model function

Updated create_model return type annotation to return type which inherits from __base__ argument.

For instance, before this PR mypy will fail on the code below:

from pydantic import BaseModel, create_model

class Point(BaseModel):
    x: int
    y: int

NewPoint = create_model('NewPoint', __base__=Point)

point = NewPoint.parse_obj(...)
point.x = 10  # mypy will fail here

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)

[codecov]

Codecov Report

Merging #2071 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #2071   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         4096      4096           
  Branches       821       821           
=========================================
  Hits          4096      4096           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8dcc87c...8725a18. Read the comment docs.

[PrettyWood]

LGTM thanks !

[samuelcolvin]

this looks good. As far as I'm aware it shouldn't be included in v1.7.2 so I won't merge it yet.

let me know if I'm missing something.

[samuelcolvin]

thanks a lot.