Python-在包装函数命名后调用包装函数

Question

I honestly don't know if this is good, bad, neutral, whatever.

def foo():
    return "foo called"

def bar():
    return "BAR CALLED"

def wrap(func):
    def _(*args, **kwargs):
        try:
            func.counter += 1
        except:
            func.counter = 0
        print "The count is %d" % func.counter
        return func(*args, **kwargs)
    return _

>>> foo = wrap(foo)
>>> bar = wrap(bar)
>>> foo()
'The count is 0'
'foo called'
>>> foo()
'The count is 1'
'foo called'
>>> bar()
'The count is 0'
'BAR CALLED'

So far, so good -- functions are just wrapped, no big deal. Here's the bit that I don't know whether to consider a feature or not.

>>> foo
<function _ at 0x100499ed8>
>>> _()
The count is 2
'foo called'
>>> bar
<function _ at 0x10049f320>
>>> _()
The count is 1
'BAR CALLED'
>>> 

Perhaps I know too little of the behind-the-scenes here, but Python has two wrapper functions in memory named _ , and a user can apparently 'switch' between them by just typing the name of the function it wraps.

Is this a feature, and if it is, what would its primary application be? Or if it is not, is this best left forgotten about, because it's just a Bad Idea to try and featurize this behavior? My journeyman guess is that this is only doable because there are not real closures in Python (which probably puts it under We're all adults here and I should not ever try to actually do this), but that's an uneducated guess.

Answer 1

That is a shortcut of the Python interpreter. The result of the last expression evaluated is assigned to _ so that you can use it in subsequent operations.

Like:

>>> 5 + 7
12
>>> _ * 2
24
>>> _ + 3
27

Please note that this will work only in an interactive shell, not in a script, and only when _ isn't already defined by you.