It’s not the walrus operator that is being abused, it’s the if
operator. You have:
None if stack[-1].append(innermost:=[]) else innermost
That use of the walrus operator is perfectly fine! All you are doing is
using the walrus as a way to keep a named reference to an expression you
have just used, which is exactly what the operator was invented for!
(This example is a little unusual only in that the expression being
captured is so simple, a plain old literal [], instead of something
complicated or expensive.)
There are other ways to get the same effect. Who needs a named
reference?
# Untested.
if this > len(stack):
stack[-1].append([]) # nest the new level
stack.append(stack[-1][-1]) # and push it
Anyway, the walrus is fine. It’s the if operator that is freaky:
something that never gets used
if something that always return False
else something
So let’s fix it!
if this > len(stack):
stack[-1].append(newlevel:=[])
stack.append(newlevel)
People who don’t like the walrus operator would prefer to put
newlevel = [] in its own statement, and honestly I agree that is
probably better. But using the walrus operator to re-use the same list
is pretty good.
We can even save another line, without using a semicolon:
if this > len(stack):
stack[-1].append(newlevel:=[]) or stack.append(newlevel)
Pretty hackish, but it’s still better than the abuse of the ternary if
operator!