如何利用 Python 闭包来编写回调函数

Question

我在亚马逊的手册页上找到了这段代码。它用作创建回调对象，这些回调对象可以作为传输模块的上传函数的参数传递：

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()

类用于保留后续调用所需的状态(self.seen_so_far即(

有没有办法将其重新实现为利用 Python 闭包来确保有状态的函数？

Answer 1

当然，一个简单的音译是这样的：

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