function pointers in python

Question

I would like to do something like the following:

def add(a, b):
 #some code
def subtract(a, b):
 #some code
operations = [add, subtract]
operations[0]( 5,3)
operations[1](5,3)

In python, is it possible to assign something like a function pointer?

• Robert Rossney: Try actually executing that code in the interactive environment and see what happens.
• S.Lott: I'm tempted to delete the silly [function-pointer] and [anonymous-methods] tags because they don't makes sense in Python. But then, this kind of question shows that Python lacks those complexities.
• Jeremy Cantrell: you're in luck, my friend, but they're neither anonymous nor unbound
• tzot: I think by "unbound functions" he meant "functions, not methods".
• S.Lott: No, "unbound functions" is a hair-splitting in C++ and "prothon" to explain functions that are not (yet) bound to a class, but could be. And Java folks have to give functions fancy-sounding names.

Answer 1

Did you try it? What you wrote works exactly as written. Functions are first-class objects in Python.

Answer 2

Python has nothing called pointers, but your code works as written. Function are first-class objects, assigned to names, and used as any other value.

You can use this to implement a Strategy pattern, for example:

def the_simple_way(a, b):
 # blah blah
def the_complicated_way(a, b):
 # blah blah
def foo(way):
 if way == 'complicated':
 doit = the_complicated_way
 else:
 doit = the_simple_way
 doit(a, b)

Or a lookup table:

def do_add(a, b):
 return a+b
def do_sub(a, b):
 return a-b
handlers = {
 'add': do_add,
 'sub': do_sub,
}
print handlers[op](a, b)

You can even grab a method bound to an object:

o = MyObject()
f = o.method
f(1, 2) # same as o.method(1, 2)

• heretoinfinity: If they are not called "function pointers", what do you call them? Just function as in my mind, a function is either the definition or its call that includes the parentheses. But I am no expert.
• Ned Batchelder: If you do this: def foo(): ...; bar = foo then foo and bar are both names referring to a function. There is no difference between them. So if foo is a function, then why isn't bar a function?

Answer 3

Just a quick note that most Python operators already have an equivalent function in the operator module.