lambda

[Ben C]

On 2006-04-21, rubbishemail at web.de <rubbishemail at web.de> wrote:
> Hello,
>
> I need your help understanding lambda (and doing it a better way
> without).
>
> f  = lambda x : x*x
> [...]
> # the idea is now to give the definition of the multiplication of
> functions and integers
> # (f * c)(xx) := f(x)*c
> [lambda xx: f(xx)*y for y in range(1,5)][0](1)
> # returns 4
> # I would expect 1*x*x = 1

If you change the 5 in range(1,5) to a 10, this returns 9.

So it looks like each of the lambda xx : f(xx) * y is getting the last
value of y.

I can do this for example:

f = lambda x : x * x
fns = [lambda xx: f(xx)*y for y in range(1,10)]
for fn in fns:
	print fn(1)

And I get 9 printed out 9 times.

It does seem a bit surprising, but I suppose if you think about it
there's only one "y"-- the one in the outer scope. This one variable is
bound 9 times, to a new value each time.

What one would need for it to work would be for each of the functions to
have a variable in its own scope. But you can't, as far as I know,
create local variables in functions defined with lambda.