On: Functional programming with Python

[aschwo]

I'm curious, on the Currying (Standard Library) slide, the author uses `attrgetter` from the `operator` module -- I've always used `getattr` to achieve the same thing. Am I missing something by not using `attrgetter`?

[walrus → aschwo]

Short answer: not really.

Long answer:

  In [1]: from operator import attrgetter

  In [2]: class Person:
     ...:     def __init__(self, name):
     ...:         self.name = name
     ...:         

  In [3]: me = Person('walrus')

  In [4]: getattr(me, 'name')
  Out[4]: 'walrus'

  In [5]: attrgetter('name')(me)
  Out[5]: 'walrus'

This is potentially useful if you're using `map`:

  In [6]: people = [me, Person('aschwo')]

  In [7]: list(map(lambda obj: getattr(obj, 'name'), people))
  Out[7]: ['walrus', 'aschwo']

  In [8]: list(map(attrgetter('name'), people))
  Out[8]: ['walrus', 'aschwo']

Really, though, the functional programming idioms don't meld too well with Python. I think this is a lot nicer:

  In [9]: [person.name for person in people]
  Out[9]: ['walrus', 'aschwo']

[andreasvc → walrus]

On the last point, a list comprehension is just a much a functional programming idiom--Python got them from Haskell! I use both in my code, whichever is shortest.

PS: map returns a list, no need to call list() on it.

[walrus → andreasvc]

In Python 3, map returns a iterator, not a list:

  In [1]: sq = lambda x: x * x
  
  In [2]: map(sq, [1,2,3,4])
  Out[2]: <builtins.map at 0x2135050>
  
  In [3]: list(_)
  Out[3]: [1, 4, 9, 16]

[apendleton → aschwo]

attrgetter takes an attribute name and returns a function that, when passed an object, returns that attribute from that object. So it's a curried getattr. These are equivalent:

f = attrgetter("some_property")

f = lambda obj: getattr(obj, "some_property")