On 7/18/2011 8:24 AM, Paul Woolcock wrote:
Partial function application (or "currying") is the act of taking a
function with two or more parameters, and applying some of the arguments
in order to make a new function. The "hello world" example for this
seems to be this:
Let's say you have a function called `add`, that takes two parameters:
>> def add(left, right):
... return left + right
Now let's say you want a function that always adds 2 to a number you
give it. You can use partial function application to do this:
>>> from functools import partial
>>> add2 = partial(add, right=2)
Now, you have a new function, `add2`, that takes one parameter:
>>> add2(4)
Or you can directly write
def add2(x): return x + 2
or more generically
def makeadder(y)
def _add(x): return x+y
add2 = makeadder(2)
functool.partial is essential a generic version of makeadder in that it
also abstract the function/operator. It is useful when one has a
function but perhaps not the source. It's limitation is that args are
frozen left to right while the above example freezes the right operand.
--
Terry Jan Reedy
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