I think the "foo | bar" syntax for Union is pretty clear, I like it! The ~foo for Optional is... not that obvious. Not sure it's a win. On Thu, 29 Aug 2019 at 13:49, Philippe Prados <philippe.prados@gmail.com> wrote:
Hello everybody,
Scala 3 propose the a new syntax for Union type. See here <https://dotty.epfl.ch/docs/reference/new-types/union-types.html>. I propose to add a similar syntax in Python.
# Operator for Union assert( int | str == Union[int,str]) assert( int | str | float == Union[int,str,float]) # Operator for Optional assert( ~int == Optional[int])
Now, it's possible to write:
def fn(bag:List[int | str], option: ~int = None) -> float | str: ...
in place of
def fn(bag:List[Option[int,str]], option: Optional[int] = None) -> Union[float,str]: ...
I think these syntaxes are more clear, and can help with the adoption of typing.
I test and implement these ideas in a two fork : One for CPython <https://github.com/pprados/cpython> and one for MyPy <https://github.com/pprados/mypy>. See the branches add_OR_to_types (for Union syntax) or add_INVERT_to_types (for Union and Optional syntax).
How I implement that ? I add the operators __or__ and __revert__ to PyType_Type. The C code is similar of :
from typing import * def type_or(self,right): return Union[self,right] type(type).__or__ = type_or
Actually, the accepted syntax for typing is :
annotation: name_type name_type: NAME (args)? args: '[' paramslist ']' paramslist: annotation (',' annotation)* [',']
I propose to extend the syntax to :
annotation: ( name_type | or_type | invert_type ) name_type: NAME (args)? args: '[' paramslist ']' paramslist: annotation (',' annotation)* [',']
or_type: name_type '|' annotation
invert_type: '~' annotation
What do you think about that ?
The draft of a PEP is here <https://github.com/pprados/peps/blob/master/pep-9999.rst>.
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