CODEWITHSUNDEEP
pythonfunctionoptional-parametersoptional-arguments
LinuxMercedes
LinuxMercedes

Reputation: 251

Assign pass to a function in Python

I have a piece of code that defines a function that takes a function as an argument, like so:

def stuff(n, f):
  f(n)

Now, I want to provide some default value of f that does nothing. So I figured I'd use pass, like so:

def stuff(n, f = None):
  if(f is None):
    f = pass
  f(n)

But this does not compile. How should I be doing this?

Upvotes: 8

Views: 2821

Answers (6)

Ivan Dives
Ivan Dives

Reputation: 517

I'd go with a

def nop(*args, **kwargs):
    pass

def algo(func=nop):
    do_something()
    func()
    do_something_else()

algo() # nop is called
algo(some_callback) # some_callback is called

IMHO looks cleaner than

if foo:
    foo()

Upvotes: 1

Alcolo47
Alcolo47

Reputation: 101

The generic noop function :

f = lambda *x,**y:None

You can call

f()
f(0,foo=0)

Upvotes: 3

Nicolas Lefebvre
Nicolas Lefebvre

Reputation: 4282

Why not simply this ?

def stuff(n, f=None):
    if f is None:
        return
    return f(n)

Upvotes: 9

Björn Pollex
Björn Pollex

Reputation: 76856

A little shorter:

def stuff(n, f=None):
  f = f or (lambda x: None)
  f(n)

Or even better:

def stuff(n, f=None):
    f(n) if f is not None else None

Upvotes: 5

Keith
Keith

Reputation: 43054

The pass is a keyword for the interpreter, a place holder for otherwise nothing. It's not an object that you can assign. You can use a no-op lambda.

f = lambda x: None

Upvotes: 19

gruszczy
gruszczy

Reputation: 42208

You can't assing empty. But you can creaty internal function, that you will assign to f.

def stuff(n, f=None):
  def empty(n):
    pass
  if f is None:
    f = empty
  f(n)

Upvotes: 4

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