Python function as a function argument?

Question

Can a Python function be an argument of another function?

Say:

def myfunc(anotherfunc, extraArgs):
    # run anotherfunc and also pass the values from extraArgs to it
    pass

So this is basically two questions:

1. Is it allowed at all?
2. And if it is, how do I use the function inside the other function? Would I need to use exec(), eval() or something like that? Never needed to mess with them.

BTW, extraArgs is a list/tuple of anotherfunc's arguments.

Answer 1

Can a Python function be an argument of another function?

Yes.

def myfunc(anotherfunc, extraArgs):
    anotherfunc(*extraArgs)

To be more specific ... with various arguments ...

>>> def x(a,b):
...     print "param 1 %s param 2 %s"%(a,b)
...
>>> def y(z,t):
...     z(*t)
...
>>> y(x,("hello","manuel"))
param 1 hello param 2 manuel
>>>

Answer 2

Here's another way using *args (and also optionally), **kwargs:

def a(x, y):
  print x, y

def b(other, function, *args, **kwargs):
  function(*args, **kwargs)
  print other

b('world', a, 'hello', 'dude')

Output

hello dude
world

Note that function, *args, **kwargs have to be in that order and have to be the last arguments to the function calling the function.

Answer 3

Functions in Python are first-class objects. But your function definition is a bit off.

def myfunc(anotherfunc, extraArgs, extraKwArgs):
  return anotherfunc(*extraArgs, **extraKwArgs)

Answer 4

Sure, that is why python implements the following methods where the first parameter is a function:

• map(function, iterable, ...) - Apply function to every item of iterable and return a list of the results.
• filter(function, iterable) - Construct a list from those elements of iterable for which function returns true.
• reduce(function, iterable[,initializer]) - Apply function of two arguments cumulatively to the items of iterable, from left to right, so as to reduce the iterable to a single value.
• lambdas

Answer 5

Function inside function: we can use the function as parameter too..

In other words, we can say an output of a function is also a reference for an object, see below how the output of inner function is referencing to the outside function like below..

def out_func(a):

  def in_func(b):
       print(a + b + b + 3)
  return in_func

obj = out_func(1)
print(obj(5))

the result will be.. 14

Hope this helps.

Answer 6

1. Yes, it's allowed.
2. You use the function as you would any other: anotherfunc(*extraArgs)

Answer 7

1. Yes. By including the function call in your input argument/s, you can call two (or more) functions at once.

For example:

def anotherfunc(inputarg1, inputarg2):
    pass
def myfunc(func = anotherfunc):
    print func

When you call myfunc, you do this:

myfunc(anotherfunc(inputarg1, inputarg2))

This will print the return value of anotherfunc.

Hope this helps!

Answer 8

def x(a):
    print(a)
    return a

def y(a):
    return a

y(x(1))

Answer 9

def x(a):
    print(a)
    return a

def y(func_to_run, a):
    return func_to_run(a)

y(x, 1)

That I think would be a more proper sample. Now what I wonder is if there is a way to code the function to use within the argument submission to another function. I believe there is in C++, but in Python I am not sure.

Answer 10

Decorators are very powerful in Python since it allows programmers to pass function as argument and can also define function inside another function.

def decorator(func):
      def insideFunction():
        print("This is inside function before execution")
        func()
      return insideFunction

def func():
    print("I am argument function")

func_obj = decorator(func) 
func_obj()

Output

• This is inside function before execution
• I am argument function