CODEWITHSUNDEEP
pythoncallbackclosures
darkpirate
darkpirate

Reputation: 722

how to leverage python closure to write callback functions

i've found this code on the man page of amazon. It is used as a to create callback objects that can be passed as argument of the upload function of the transfer module:

class ProgressPercentage(object):

def __init__(self, filename):
    self._filename = filename
    self._size = float(os.path.getsize(filename))
    self._seen_so_far = 0
    self._lock = threading.Lock()

def __call__(self, bytes_amount):
    # To simplify we'll assume this is hooked up
    # to a single filename.
    with self._lock:
        self._seen_so_far += bytes_amount
        percentage = (self._seen_so_far / self._size) * 100
        sys.stdout.write(
            "\r%s  %s / %s  (%.2f%%)" % (
                self._filename, self._seen_so_far, self._size,
                percentage))
        sys.stdout.flush()

a class is used to retain the state necessary for the subsequent calls (self.seen_so_far i.e.)

is there a way to reimplement this as a function taking advantage of python closure to ensure statefulness ?

Upvotes: 0

Views: 1233

Answers (1)

juanpa.arrivillaga
juanpa.arrivillaga

Reputation: 96246

Sure, a straightforward transliteration would be something like:

def ProgressPrecentage(filename):
    size = os.path.getsize(filename)
    seen_so_far = 0
    lock = threading.Lock()
    def worker(bytes_amount):
        nonlocal seen_so_far
        with lock:
            seen_so_far += bytes_amount
            percentage = (seen_so_far / size)*100
            msg = "\r%s  %s / %s  (%.2f%%)" % (
                filename, seen_so_far, size, percentage
            )
            sys.stdout.write(msg)
            sys.stdout.flush()
    return worker

Upvotes: 2

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