Python function composition

function-composition, python

Solution

`append` does in-place addition, as Ignacio Vazquez-Abrams said (well, implied) -- so, while you could fix that by just adding a `return` to your function, it would have the side-effect of changing the argument it was passed, too:

@composable
def f4(a):
    a.append(0)
    return a

It would be best to use the following even more concise code which also creates and returns a new object:

@composable
def f4(a):
  return a + [0]

Problem

I've tried to implement function composition with nice syntax and here is what I've got: ``` from functools import partial class _compfunc(partial): def __lshift__(self, y): f = lambda *args, **kwargs: self.func(y(*args, **kwargs)) return _compfunc(f) def __rshift__(self, y): f = lambda *args, **kwargs: y(self.func(*args, **kwargs)) return _compfunc(f) def composable(f): return _compfunc(f) @composable def f1(x): return x * 2 @composable def f2(x): return x + 3 @composable def f3(x): return (-1) * x print f1(2) #4 print f2(2) #5 print (f1 << f2 << f1)(2) #14 print (f3 >> f2)(2) #1 print (f2 >> f3)(2) #-5 ``` It works fine with integers, but fails on lists/tuples: ``` @composable def f4(a): a.append(0) print f4([1, 2]) #None ``` Where is a mistake?

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