Python lambda *args, **kwargs: 无
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lambda *args, **kwargs: None
提问by Scruffy
consider:
考虑：
blank_fn = lambda *args, **kwargs: None
def callback(x, y, z=''):
print x, y, z
def perform_task(callback=blank_fn):
print 'doing stuff'
callback('x', 'y', z='z' )
The motivation for doing it this way is I don't have to put in logic to check if callback has been assigned because it defaults to blank_fn which just does nothing.
这样做的动机是我不必放入逻辑来检查是否已分配回调，因为它默认为 blank_fn 什么也不做。
This works, but is there some reason I shouldn't do it? Is it pythonic? Is there a better way to do it? Is there a built-in for:
这有效，但有什么理由我不应该这样做吗？它是pythonic吗？有没有更好的方法来做到这一点？是否有内置的：
lambda *args, **kwargs: None
采纳答案by Chris Barker
According to PEP8, you should "Always use a def statement instead of an assignment statement that binds a lambda expression directly to a name." So, one thing I would change is:
根据PEP8，您应该“始终使用 def 语句而不是将 lambda 表达式直接绑定到名称的赋值语句。” 所以，我要改变的一件事是：
def blank_fn(*args, **kwargs):
pass
However, I think a more pythonic way to do this is:
但是，我认为更pythonic的方法是：
def perform_task(callback=None):
print 'doing stuff'
if callback is not None:
callback('x', 'y', z='z')
There shouldn't be any need to call a function that does nothing. Truth value testing is cheaper than function calling.
没有必要调用一个什么都不做的函数。真值测试比函数调用便宜。
def do_nothing(*args, **kwargs): pass
def do_something(arg, callback=do_nothing):
a = 1 + 2
callback('z', z='z')
def do_something_else(arg, callback=None):
a = 1 + 2
if callback is not None:
callback('z', z='z')
%timeit do_something(3)
1000000 loops, best of 3: 644 ns per loop
%timeit do_something_else(3)
1000000 loops, best of 3: 292 ns per loop
回答by DRendar
I think the previous answer is superior, as it provides a better way to accomplish what the OP wanted to do.
我认为之前的答案更胜一筹，因为它提供了一种更好的方法来完成 OP 想要做的事情。
However there may arguably be circumstances when you want a noop function when testing, or if you are monkey patching something.
然而，当您在测试时想要一个 noop 函数，或者如果您正在修补某些东西时，可能会出现一些情况。
So to answer the OP Question as asked, you can use Mock:
因此，要按要求回答 OP 问题，您可以使用 Mock：
In [1]: from mock import Mock
In [2]: blank_fn = Mock(return_value=None)
In [3]: blank_fn()
In [4]: blank_fn("foo")
In [5]: blank_fn(bar="foo")
In [6]: blank_fn("foobar", bar="foo")
In [7]:
