如何利用python闭包编写回调函数

Question

我在亚马逊的手册页上找到了这个代码。 它用作创建回调对象的函数，回调对象可以作为transfer module的upload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 (到目前为止还没见过i、 e.）

有没有办法将其重新实现为一个函数，利用python闭包来确保状态性？你知道吗

Answer 1

当然，直接的音译应该是这样的：

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