[Python-Dev] The `for y in [x]` idiom in comprehensions

[Stephen J. Turnbull]

Barry Warsaw writes:

 > My questions are 1) will this become idiomatic enough to be able to
 > understand at a glance what is going on,

Is it similar enough to

    def f(x=[0]):

which is sometimes seen as a way to produce a mutable default value
for function arguments, to be "idiomatic"?

 > rather than having to pause to reason about what that 1-element
 > list-like syntax actually means, and 2) will this encourage even
 > more complicated comprehensions that are less readable than just
 > expanding the code into a for-loop?

Of course it will encourage more complicated comprehensions, and we
know that complexity is less readable.  On the other hand, a for loop
with a temporary variable will take up at least 3 statements vs. a
one-statement comprehension.

I don't have an opinion about the equities there.  I myself will
likely use the [(y, f(y)) for x in xs for y in costly(x)] idiom very
occasionally, with emphasis on "very" (for almost all "costly"
functions I might use that's the Knuthian root of error).  But I don't
know how others feel about it.

Steve