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.
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
