如何利用python闭包编写回调函数 [英] how to leverage python closure to write callback functions
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问题描述
我在亚马逊的手册页上找到了此代码.它用作创建回调对象,可以将其作为
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()
使用一个类来保留后续调用所需的状态(即self.seen_so_far)
a class is used to retain the state necessary for the subsequent calls (self.seen_so_far i.e.)
是否有一种方法可以重新实现为利用python闭包以确保有状态性的功能?
is there a way to reimplement this as a function taking advantage of python closure to ensure statefulness ?
推荐答案
当然,简单的音译应该是这样的:
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
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