On May 9, 12:12 pm, "Gabriel Genellina" <[EMAIL PROTECTED]>
wrote:
> En Thu, 08 May 2008 22:57:03 -0300,
> <[EMAIL PROTECTED]> escribió:
>
>
>
> > On May 8, 6:11 pm, Duncan Booth <[EMAIL PROTECTED]> wrote:
>
> >> No, no, no, no, no!
> > Geez. Go easy.
> >> You have got it entirely wrong here. Your XOR function simply
> [...]
> > Pardon my tetchiness, but it is a little hard to receive such blunt
> > and inflexible replies to my posts.
>
> Don't take it so seriously. I would have written a reply in the same tone.
> Weeds must be uprooted early :)
>
> > Both the responses offer lambda free alternatives. That's fine, and
> > given the terse documentation and problems that I had understanding
> > them, I would agree. So what applications are lambdas suited to? I
> > think the parameterised function model is one.
> > What else?
>
> It should be clear now that lambda is just a shortcut for defining a
> normal function using "def", except it has no name, and it can handle
> expressions only (no statements).
> So you never *need* a lambda. But in a few cases they're useful:
>
> - Most GUIs are event-driven, and let you bind a function (or any other
> callable object) to be executed when certain event happens (by example,
> when certain button is pressed, or a menu item is selected). Usually an
> instance method is used: Button("Total", onclick=self.calculate_total).
> Suppose you're developing a calculator; the ten buttons labeled '0' to '9'
> should inserte the corresponding digit. To do that, you should write ten
> functions insert_digit_0 to insert_digit_9 (and they would be
> one-line-functions: insert_digit('0') ... insert_digit('9')). Too boring :(
> The usual idiom is something like this:
> Button("0", onclick=lambda: self.insert_digit('0'))
> Button("5", onclick=lambda: self.insert_digit('5'))
>
> - To write an expression that is to be evaluated lazily (perhaps only if
> certain other conditions are met). Older Python versions didn't have a
> conditional expression like C's :? ternary operator, and one possible way
> to emulate it is this:
>
> def iif(cond, if_true, if_false):
> if cond:
> return if_true()
> else:
> return if_false()
>
> iff(x!=2, lambda: 1/(x-2), lambda: 100)
>
> You can't write iff(x!=2, 1/(x-2), 100) because arguments are evaluated
> before the function is called, and with x=2 you get an error.
>
Calling iff would give a NameError. I wonder why... perhaps because
iif is so iffy?
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