Re: [Tutor] function that returns a fn

[Kent Johnson]

Yes, it really is that simple. :-)
A common example is a function that makes a function which adds a constant to 
its argument:
>>> def makeadder(n):
...   def adder(x):
...     return x + n
...   return adder
...
Make a function that adds 3 to its argument...note there is no special syntax for the return, just 
assign to a name
>>> add3 = makeadder(3)

add3 is a function:
>>> add3
<function adder at 0x008D68F0>
>>> add3(4)
7
Make another function to add 5:
>>> add5 = makeadder(5)
>>> add5(10)
15
add3 still works, it is a separate function with its own binding of n:
>>> add3(2)
5
Kent
Nandan wrote:
I'm looking for resources to help me with a fn that returns a fn after
binding one of its arguments (aka currying, like the bind1st of C++)
Considering Python syntax is quite straightforward, this is my first try:
def getjlistrenderer(opname):
        def listrender():
                # use opname, eg ops=getlist(opname)
                # or set local fn variable
                return renderer;
        return listrender;
        #?or f=listrender(); return f;
Is it really as simple as this? Or will I always return the same function
definition? I need it to return a 'new' function for each call to
getjlistrender() .. do I need to create a new fn with f=listrender() ?
No, this is a call to listrender, it will return the renderer object not a 
function.
Any pointers to pages/books etc. appreciated. I am looking through my
books too, but thought I'd get some more pointers as well. Web searching
so far only shows lambda, which is one-liner, and that won't do.
There are several currying recipes in the Python Cookbook:
http://aspn.activestate.com/ASPN/search?query=curry&x=0&y=0&section=PYTHONCKBK&type=Subsection
Searching the cookbook for 'closure' also gives some recipes that might be of 
interest.
Kent
Thanks!
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