What is more pythonic: trivial lambda or None?

When a function accepts a function argument (or a class has a function slot), there is a choice between two approaches:

def foo(..., my_func=None, ...):
    ...
    if my_func:
        my_func(...)
    ...

and

def foo(..., my_func=(lambda ...: None), ...):
    ...
    my_func(...)
    ...

What is more Pythonic/clear/readable?

What is faster - an extra boolean check or a trivial function call?

Solution

When using this:

>>> def bar():
...     print("Goodbye, World!")
...

I find this very readable:

>>> def foo(my_func = lambda : None):
...     my_func()
...
>>> foo()
>>> foo(bar)
Goodbye, World!

I find this pointlessly annoying

>>> def baz(my_func = None):
...     if my_func is not None:
...         my_func()
...
>>> baz()
>>> baz(bar)
Goodbye, World!

Try to keep None checks out of your life. Use None when you want it to do what it does well: blow up in your face. Don't ask it to be quiet. One way or another it's going to create annoying noise if you use it.

What is faster - an extra boolean check or a trivial function call?

Why, in Gods name, do you care?

For the record, I find this readable but overly permissive:

>>> def buz(my_func = lambda **k:None):
...     my_func()
...
>>> buz(bar)
Goodbye, World!