python function list chained executing?

Question

Hi,

In python I defined functions:

def foo_1(p): return p + 1
def foo_2(p): return p + 1
def foo_3(p): return p + 1
def foo_4(p): return p + 1
def foo_5(p): return p + 1

I need execute those function as a chain may like this:

foo_1(foo_2(foo_3(foo_4(foo_5(1)))))

May I know if I can push the functions into a list then execute those functions as a chain, also maybe I can give an executing sequence?

lf = [Null,foo_1,foo_2,foo_3,foo_4,foo_5]  # Null is for +1 issue here

def execu(lst, seq, raw_para):
    # in some way

execu(lf,(1,2,3,4,5), 1)   # = foo_1(foo_2(foo_3(foo_4(foo_5(1)))))
execu(lf,(1,2,3), 1)       # = foo_1(foo_2(foo_3(1)))
execu(lf,(3,3,3), 1)       # = foo_3(foo_3(foo_3(1)))

Thanks!

Rgs,

KC

Answer 1

def execu(lst, seq, raw_para):
  return reduce(lambda x, y: y(x), reversed(operator.itemgetter(*seq)(lst)), raw_para)

Answer 2

You can use reduce for this:

reduce(lambda x, y: y(x), list_of_functions, initial_value)

Like so:

reduce(lambda x, y: y(x), reversed([foo_1, foo_2, foo_3, ...]), 1)

Note that If you want to apply the functions in the order of foo_1(foo_2(etc...)), you have to make sure that foo_1 is the last element of the list of functions. Therefore I use reversed in the latter example.

Answer 3

No need for "Null" in "lf".

def execu(lst, seq, raw_para):  
    para=raw_para  
    for i in reversed(seq):  
        para=lst[i](para)
    return para