explain this function to me, lambda confusion

[Gabriel Genellina]

En Wed, 07 May 2008 18:38:15 -0300, globalrev <skanemupp at yahoo.se>  
escribió:

> i have a rough understanding of lambda but so far only have found use
> for it once(in tkinter when passing lambda as an argument i could
> circumvent some tricky stuff).
> what is the point of the following function?
>
> def addn(n):
> 		return lambda x,inc=n: x+inc

lambda is just a shortcut for defining a function without a name.
The above code is the same as:

def addn(n):
     def inner(x, inc=n):
         return x+inc
     return inner

It should be clear now that addn returns a function. addn is a "function  
factory": builds functions by request. You ask it "give me a function that  
adds 5" and addn returns that function.

> if i do addn(5) it returns
>
>>>> addn(5)
> <function <lambda> at 0x01D81830>

If you try the other version, you would get:

<function inner at 0x00A3B970>

It's the same thing, except that lambda has no name.

> ok? so what do i write to make it actually do something.

adder5 = addn(5)
adder5(3)
-> 8

>  and is the
> inc=n necessary i cant do x+n?

Yes, you can, but there is a subtle difference that's hard to explain, and  
in this case it's absolutely irrelevant. Using inc=n "does the right  
thing" as it's a bit more efficient too.

-- 
Gabriel Genellina