Łukasz Langa writes:
On 25 Apr, 2018, at 5:20 PM, Chris Angelico rosuav@gmail.com wrote:
You're claiming that := is nicer in this situation because it's
less
prominent than regular assignment and thus doesn't suggest that the name
stays visible later.
FWIW, I read what he wrote as "assuming buf is not going to be used later", and thus took a more nuanced idea from it: Use a separate statement when you do use it later, and use a binding expression when its scope is in fact only that line.
BTW, I don't find the "it could be misused, so it will be misused" argument persuasive. I agree it's true, but don't think it matters, per the "consenting adults" principle, since binding expressions have other, important, use cases.
We could add a statement to PEP 8 mildly deprecating this particular use. How about this:
In some examples, the binding expression is used in function
arguments where one argument depends on an earlier one, such as
foo(buffer=(buf := [None]*get_size()), size=len(buf))
In examples like this one, it is preferable where possible to
refactor the function to calculate the dependent variable itself,
or to use an assignment statement to define the bound variable.
The latter style is *strongly* preferred when the bound variable
will be used later in the scope.
Steve