Basedmypy -- Based Static Typing for Python
===========================================
Ever tried to use pythons type system and thought to yourself "This doesn't seem based".
Well fret no longer as basedmypy got you covered!
Baseline
--------
Basedmypy has baseline, baseline is based! It allows you to adopt new strictness or features
without the burden of fixing up every usage, just save all current errors to the baseline
file and deal with them later.
.. code-block:: python
def foo(a):
print(a)
.. code-block:: bash
> mypy test.py
error: missing typehints !!!!!
Epic fail bro!
> mypy --write-baseline test.py
test.py:1:1: error: Function is missing a type annotation for one or more arguments [no-untyped-def]
Baseline successfully written to .mypy/baseline.json
> mypy test.py
Success: no issues found in 1 source file
Then on subsequent runs the existing errors will be filtered out.
.. code-block:: python
def foo(a):
print(a)
def bar(b: str, c: int) -> bool:
return b + c
.. code-block:: bash
> mypy test.py
test.py:4:5: error: Returning Any from function declared to return "bool" [no-any-return]
test.py:4:16: error: Unsupported operand types for + ("str" and "int") [operator]
Found 2 errors in 1 file (checked 1 source file)
Intersection Types
------------------
Using the ``&`` operator or ``basedtyping.Intersection`` you can denote intersection types.
.. code-block:: python
class Growable(ABC, Generic[T]):
@abstractmethod
def add(self, item: T): ...
class Resettable(ABC):
@abstractmethod
def reset(self): ...
def f(x: Resettable & Growable[str]):
x.reset()
x.add("first")
Type Joins
----------
Mypy joins types like so:
.. code-block:: python
a: int
b: str
reveal_type(a if bool() else b) # Revealed type is "builtins.object"
Basedmypy joins types into unions instead:
.. code-block:: python
a: int
b: str
reveal_type(a if bool() else b) # Revealed type is "int | str"
Bare Literals
-------------
``Literal`` is so cumbersome! just use a bare literal instead.
.. code-block:: python
class Color(Enum):
RED = auto()
a: 1 | 2
b: True | Color.RED
Default Return Type
-------------------
With the ``default_return`` option, the default return type of functions becomes ``None`` instead of `Any`.
.. code-block:: python
def f(name: str):
print(f"Hello, {name}!")
reveal_type(f) # (str) -> None
Nested TypeVars
---------------
With nested ``TypeVar``\s you are able to have functions with polymorphic generic parameters.
.. code-block:: python
E = TypeVar("E")
I = TypeVar("I", bound=Iterable[E])
def foo(i: I, e: E) -> I:
assert e not in i
return i
reveal_type(foo(["based"], "mypy")) # N: Revealed type is "list[str]"
reveal_type(foo({1, 2}, 3)) # N: Revealed type is "set[int]"
Overload Implementation Inference
---------------------------------
Specifying types in overload implementations is completely redundant! basedmypy will infer them.
.. code-block:: python
@overload
def f(a: int) -> str: ...
@overload
def f(a: str) -> int: ...
def f(a):
reveal_type(a) # int | str
return None # error: expected str | int
class A:
@property
def foo(self) -> int: ...
@foo.setter
def foo(self, value): ... # no need for annotations
Infer Function Parameters
-------------------------
Infer the type of a function parameter from it's default value.
.. code-block:: python
def f(a=1, b=True):
reveal_type((a, b)) # (int, bool)
Better Types in Messages
------------------------
.. code-block:: python
T = TypeVar("T", bound=int)
def f(a: T, b: list[str | 1 | 2]) -> Never:
reveal_type((a, b))
reveal_type(f)
Mypy shows::
Revealed type is "Tuple[T`-1, Union[builtins.str, Literal[1], Literal[2]]]"
Revealed type is "def [T <: builtins.int] (a: T`-1, b: Union[builtins.str, Literal[1], Literal[2]]) -> <nothing>"
Basedmypy shows::
Revealed type is "(T@f, str | 1 | 2)"
Revealed type is "def [T: int] (a: T, b: str | 1 | 2) -> Never"
Ignore Unused Type Ignores
--------------------------
In code that is targeting multiple versions of python or multiple platforms it is difficult
to work with `type: ignore` comments and use the `warn_unused_ignore` option.
The ``unused-ignore`` error code can be used for this situation.
.. code-block:: python
if sys.platform != "linux":
foo() # type: ignore[misc, unused-ignore]