mypy_numpy_example.py

# Copyright 2017 Google LLC.

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

# https://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from typing import Generic, TypeVar, Type, Union


# toy version of the NumPy type hierarchy
class generic(object):
    pass

class floating(generic):
    pass

class float64(floating):
    pass

class float32(floating):
    pass


D = TypeVar('D', bound=generic)


# toy version of np.dtype
class DType(Generic[D]):
    def __init__(self, type_: 'Union[Type[D], DType[D]]') -> None:
        if isinstance(type_, DType):
            type_ = type_.type
        self._type = type_

    @property
    def type(self) -> Type[D]:
        return self._type

DTypeLike = Union[Type[D], DType[D]]


# toy version of np.ndarray
class NDArray(Generic[D]):
    def __init__(self, dtype: DTypeLike) -> None:
        self._dtype = DType(dtype)

    @property
    def dtype(self) -> DType[D]:
        return self._dtype


def empty_flexible(dtype: DTypeLike[D]) -> NDArray[D]:
    return NDArray(dtype)

def empty_dtype_only(dtype: DType[D]) -> NDArray[D]:
    return NDArray(dtype)

def empty_generic_only(dtype: Type[D]) -> NDArray[D]:
    return NDArray(dtype)

# Tests

# All these typing errors should be caught by mypy

def invalid_convert(array: NDArray[float32]) -> NDArray[float64]:
    return array

def invalid_create_dtype_only() -> NDArray[float64]:
    return empty_dtype_only(DType(float32))

def invalid_create_flexible_dtype() -> NDArray[float64]:
    return empty_flexible(DType(float32))

def invalid_create_flexible_generic() -> NDArray[float64]:
    return empty_flexible(float32)  # mypy DOES NOT catch this

def invalid_create_generic_only() -> NDArray[float64]:
    return empty_generic_only(float32)

# These errors should pass

def valid_create_dtype_only() -> NDArray[float64]:
    return empty_dtype_only(DType(float64))

def valid_create_flexible_generic() -> NDArray[float64]:
    return empty_flexible(float64)

def valid_create_flexible_dtype() -> NDArray[float64]:
    return empty_flexible(DType(float64))

def valid_create_generic_only() -> NDArray[float64]:
    return empty_generic_only(float64)