Function name in parentheses after function call in Python

Question

I ran into these lines of code in the QPYTHON Android app. They are part of a sample that uses the Bottle module to create a simple Web server that seems to work fine.

app = Bottle()
app.route('/', method='GET')(home)
app.route('/__exit', method=['GET','HEAD'])(__exit)
app.route('/__ping', method=['GET','HEAD'])(__ping)
app.route('/assets/<filepath:path>', method='GET')(server_static)

Now, I know that all the functions in parentheses after the call have already been wrapped with the @route decorator above this. For example:

@route('/__ping')
def __ping():
    return "ok"

But I have no idea what putting things in parentheses after other things does in Python, and after trying a hundred different permutations of "functions in parentheses after functions" I gave up.

I throw myself on the mercy of the Exchange.

Answer 1

This:

app.route('/', method='GET')(home)

... Is the same as this:

func = app.route('/', method='GET')
func(home)

In other words, app.route(...) returns a function, which is then called.

Answer 2

def a():
    def b(arg):
        return arg * 2
    return b

print(a()(5))

c = a()
print(c(5))

Output:
10
10

You are basically providing an argument for the function within the function, a.k.a inner function