Às 23:56 de 23/10/22, Cameron Simpson escreveu:
On 23Oct2022 21:36, Paulo da Silva
<p_d_a_s_i_l_v_a...@nonetnoaddress.pt> wrote:
I am in the process of "typing" of some of my scripts.
Using it should help a lot to avoid some errors.
But this is new for me and I'm facing some problems.
Let's I have the following code (please don't look at the program
content):
f=None # mypy naturally assumes Optional(int) because later, at open,
it is assigned an int.
..
if f is None:
f=os.open(...
..
if f is not None:
os.write(f, ...)
..
if f is not None:
os.close(f)
When I use mypy, it claims
Argument 1 to "write" has incompatible type "Optional[int]"; expected
"int"
Argument 1 to "close" has incompatible type "Optional[int]"; expected
"int"
How to solve this?
Is there a way to specify that when calling os.open f is an int only?
I use None a lot for specify uninitialized vars.
Maybe you shouldn't. The other way is to just not initialise the var at
all. You could then just specify a type. Example:
Python 3.8.13 (default, Aug 11 2022, 15:46:53)
[Clang 12.0.0 (clang-1200.0.32.29)] on darwin
Type "help", "copyright", "credits" or "license" for more
information.
>>> f:int
>>> f
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'f' is not defined
>>>
So now `f` has `int` type definitely (for `mypy`'s purposes), and if
used before assignment raises a distinctive error (versus having the
value `None`, which you might then pass around, and perhaps successfully
use in some contexts).
It is probably better on the whole to specify types up front rather than
relying on `mypy` or similar to infer them. That way (a) you're stating
your intent and (b) not relying on an inferred type, which if you've got
bugs may be inferred _wrong_. If `mypy` infers a type incorrectly all
the subsequent checks will also be flawed, perhaps subtly.
Yes.
I also use to make f unavailable (f=None) when something goes wrong and
I don't want to stop the script but of course I could use "del f". I
also need to care about using "try", which might be better than "if" tests.
A thing to think of ...
Thanks.
Paulo
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