More Features

Legacy Mode (--legacy)

Alters the configuration of basedmypy to be much more similar to mypy, it is not completely compatible though, and baseline functionality is still active.
To disable the baseline, invoke basedmypy specifying the baseline file as an empty string: mypy --baseline-file= src

Default Return Type of None (default_return)

Causes an unannotated return type to be inferred as None.

def foo(i: int):
  print(i)

reveal_type(foo)  # revealed type is "def(int)"

It is recommended to only apply this option in the specific modules that will use it, as partially typed third party code can cause problems.

[[tool.mypy-overrides]]
module = ["mypackage.*"]
default_return = true

This plays conservatively with allow_untyped_defs and allow_incomplete_defs

# mypy: default-return allow-incomplete-defs allow-untyped-defs
def foo(a, b): ... # def(Any, Any) -> Any
def bar(a: int, b): ... # def(int, Any) -> None

Ignore Unused Ignores (type: ignore[X, unused-ignore])

Often when dealing with multi-platform code, type ignores produce false positives:

import sys

if sys.platform != "linux":
  foo()  # type: ignore[misc]

> mypy .
main.py:4: error: Unused "type: ignore" comment
Found 1 error in 1 file (checked 1 source file)

In basedmypy you can add the ignore code unused-ignore to ignore the unused ignore error:

import sys

if sys.platform != "linux":
  foo()  # type: ignore[misc, unused-ignore]

> mypy .
Success: no issues found in 1 source file

Nonlocal Partial Types (--nonlocal-partial-types)

The --local-partial-types flag in mypy is confusing, so in basedmypy it's removed in favor of the inverse --nonlocal-partial-types