On Wed, Feb 10, 2016 at 10:01 AM, Phil Thompson phil@riverbankcomputing.com wrote:
On 10 Feb 2016, at 5:52 pm, Guido van Rossum guido@python.org wrote:
[...]
That should do it, thanks. A followup question...
Is...
def foo(bar: str = Optional[str])...valid? In other words, bar can be omitted, but if specified must be a str or None?
The syntax you gave makes no sense (the default value shouldn't be a type) but to do what your words describe you can do
def foo(bar: Optional[str] = ...): ...
That's literally what you would put in the stub file (the ... are literal ellipses).
In a .py file you'd have to specify a concrete default value. If your concrete default is neither str nor None you'd have to use cast(str, default_value), e.g.
_NO_VALUE = object() # marker
def foo(bar: Optional[str] = cast(str, _NO_VALUE)): ...implementation...
Now the implementation can distinguish between foo(), foo(None) and foo('').