On 24/10/2022 05:19, Chris Angelico wrote:
On Mon, 24 Oct 2022 at 14:15, Dan Stromberg <drsali...@gmail.com> wrote:
I've found that mypy understands simple assert statements.
So if you:
if f is not None:
assert f is not None
os.write(f, ...)
You might be in good shape.
Why can't it simply understand the if statement?
Could it be that this specific problem is fixed in current mypy?
I get
$ type .\tmp.py
import os
f = None
if f is None:
f = os.open("tmp.txt", os.O_RDWR|os.O_CREAT)
os.write(f, b"yadda")
$ mypy tmp.py
Success: no issues found in 1 source file
My attempt to verify that
if name is None: ...
is recognized:
$ type .\tmp2.py
import os
import random
f = None
if random.randrange(2):
f = os.open("tmp.txt", os.O_RDWR|os.O_CREAT)
os.write(f, b"yadda")
$ mypy tmp2.py
tmp2.py:7: error: Argument 1 to "write" has incompatible type
"Optional[int]"; expected "int"
Found 1 error in 1 file (checked 1 source file)
$ mypy --version
mypy 0.982 (compiled: yes)
$
I'm not a fan of
coddling a type system like this. The entire point of type checking is
to help you find bugs more efficiently, so if you have to repeat
yourself every time you do these kinds of checks just so that mypy is
satisfied, that's counter-productive (case in point: what happens if
you say "if fn is not None: assert f is not None"? Now you've
introduced a bug just to deal with the type system).
ChrisA
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