[Python-ideas] Function composition (was no subject)

[Ron Adam]

On 05/10/2015 05:57 AM, Steven D'Aprano wrote:
> There's lots of code that assumes that a tuple of functions is a
> sequence:
>
> for f in (len, str, ord, chr, repr):
>      test(f)
>
> so we would need to keep that. But we don't want a composed function to
> be a sequence, any more than we want a partial or a regular function to
> be sequences. If I pass you a Composed object, and you try slicing it,
> that should be an error.


It seems to me a linked list of composed objects works (rather than a 
sequence).  It's easier to understand what is going on in it.


from functools import partial
from operator import *
from statistics import mean

def root(x):
     return x ** .5

def square(x):
     return x ** 2

class CF:
     def __init__(self, f, *rest):
         if isinstance(f, tuple):
             self.f = partial(*f)
         else:
             self.f = f
         if rest:
             self.child = CF(*rest)
         else:
             self.child = None
     def __call__(self, data):
         if self.child == None:
             return self.f(data)
         return self.f(self.child(data))
     def __repr__(self):
         if self.child != None:
             s = repr(self.child)
         else:
             s = "CS()"
         return s[:3] + ("%s, " % repr(self.f)) + s[3:]


CF(print, root, mean, (map, square)) ([4, 9, 16])


Prints:
10.847426730181986