[Python-Dev] PEP 572: Assignment Expressions

[Anthony Flury]

I am entirely new to this list, but if I can I would like share my 
comments :

  * I do think this proposal <target> := <value> has merit in my
    opinion; it does make some code more readable.

  * I think readability is only improved if :

      * target is restricted to a simple name - I don't see a benefit in
        more complex targets
      * chaining is not allowed - I think the construct :

                 while (line := input.read_row()) is not None:
                         process_line(line)

             Is readable, but :

                 while (current_line := line := input.read_row()) is not
    None:
                         line = process_line(line)

           is not obvious - and certainly isn't any more obvious than :

                 while (line := input.read_row()) is not None:
                         current_line = line
                         line = process_line(line)

  * The current expectations of how comprehensions work should also be
    honored; I don't claim to have fully followed all of the discussions
    around this, but it seems to me that comprehensions work in a
    particular way because of a concerted effect (especially in Python
    3) to make them that way. They are self contained and don't leak
    values in their containing scope. Similarly I think that setting
    variables within a comprehension is just for the benefit of readable
    code within the comprehension - i.e. :

		stuff = [[y, x/y] for x in range(5) for y in [f(x)]]

                 can become :

stuff = [[y := f(x), x/y] for x in range(5)]

So - overall from me a conditional +1 - conditions as above; if they are 
not possible then -1 from me.

-- 
Anthony Flury
email : *Anthony.flury at btinternet.com*
Twitter : *@TonyFlury <https://twitter.com/TonyFlury/>*