[Python-Dev] any support for a methodcaller HOF? (original) (raw)

Giovanni Bajo rasky at develer.com
Fri Feb 3 20:05:42 CET 2006

Robert Brewer <fumanchu at amor.org> wrote:

The word "execution" to me implies "statements", and although some functions somewhere are called behind the scenes to evaluate any expression, the lambda (and its potential successors) differ from "def" by not allowing statements. They may be used to "defer execution" but to me, their value lies in being static expressions--object instances which are portable and introspectable.

This is where LINQ [1] is taking off: expressions are declared with "var" (in C#). I used Expression() in Dejavu [2] for the same reasons (before LINQ came along ;), and am using it to build SQL from Python lambdas. I had to use lambda because that's Python's only builtin support for expressions-as-objects at the moment, but I'd like to see Python grow a syntax like:

e = expr(x: x + 1)

I see what you mean, but in a way you're still agreeing with me :) Your expression-as-objects proposal is very clever, but to me (and as far as this thread is concerned) it still allows to write a "decorated" piece of code (expression), pass it around, and execute (evaluate) it later. This is what I (and others) mainly use lambda for, and your expr() thing would still serve me well. Instead, itemgetter() and friends are going to a different direction (the expression which is later evaluated is not clearly expressed in familiar Python terms), and that's what I find inconvenient.

Giovanni Bajo

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