What do double parentheses mean in a function call? e.g. func(stuff)(stuff)?

Question

Original title:

"Help me understand this weird Python idiom? sys.stdout = codecs.getwriter(\'utf-8\')(sys.stdout)"

Answer 1

Calling the wrapper function with the double parentheses of python flexibility .

Example

1- funcWrapper

def funcwrapper(y):
    def abc(x):
        return x * y + 1
    return abc

result = funcwrapper(3)(5)
print(result)

2- funcWrapper

def xyz(z):
    return z + 1

def funcwrapper(y):
    def abc(x):
        return x * y + 1
    return abc

result = funcwrapper(3)(xyz(4))
print(result)

Answer 2

.getwriter returns a functioncallable object; you are merely calling it in the same line.

Example:

def returnFunction():
    def myFunction():
        print('hello!')
    return myFunction

Demo:

>>> returnFunction()()
hello!

You could have alternatively done:

>>> result = returnFunction()
>>> result()
hello!

---

Visualization:

evaluation step 0: returnSomeFunction()()
evaluation step 1: |<-somefunction>-->|()
evaluation step 2: |<----result-------->|

Answer 3

codecs.getwriter('utf-8') returns a class with StreamWriter behaviour and whose objects can be initialized with a stream.

>>> codecs.getwriter('utf-8')
<class encodings.utf_8.StreamWriter at 0x1004b28f0>

Thus, you are doing something similar to:

sys.stdout = StreamWriter(sys.stdout)