On 10/28/2011 2:10 PM, Michael McGlothlin wrote:
I'm trying to generate a list of values
Better to think of a sequence of values, whether materialized as a
'list' or not.
where each value is dependent
on the previous value in the list and this bit of code needs to be
repeatedly so I'd like it to be fast. It doesn't seem that
comprehensions will work as each pass needs to take the result of the
previous pass as it's argument. map() doesn't seem likely. filter() or
Comprehensions combine map and filter, both of which conceptually work
on each item of a pre-existing list independently. (I am aware that the
function passed can stash away values to create dependence.
reduce() seem workable but not very clean. Is there a good way to do
this? About the best I can get is this:
l = [ func ( start ) ]
f = lambda a: func ( l[-1] ) or a
filter ( f, range ( big_number, -1, -1 ) )
I guess I'm looking for something more like:
l = do ( lambda a: func ( a ), big_number, start )
Something like
def do(func, N, value):
yield value
for i in range(1,N):
value = func(value)
yield value
?
For more generality, make func a function of both value and i.
If you need a list, "l = list(do(f,N,x))", but if you do not, you can do
"for item in do(f,N,x):" and skip making the list.
--
Terry Jan Reedy
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