Python - 在 Class 實例中調用多個外部函數

Question

我有一個腳本來監視文件的變化，如果發生它應該觸發一些動作。 這些動作來自 Class 外部定義的兩個函數。 在 Class 中，我定義了部分代碼來查找文件中的更改。 我無法弄清楚如何在 Class arguments 中傳遞兩個函數。 這是我的腳本的簡化部分：

import time, os

watch_file = 'my_file.txt'

def first_action():
    print('First action called')

def second_action():
    print('Second action called')

class Watcher():
    def __init__(self, watch_file, first_action=None, second_action=None):
        self._cached_stamp = 0
        self.filename = watch_file
        self.first_action = first_action
        self.second_action = second_action

    # Look for changes in 'my_file.txt'
    def look(self):
        stamp = os.stat(self.filename).st_mtime
        if stamp != self._cached_stamp:
            self._cached_stamp = stamp
            # File has changed, so do something...
            print('File changed')
            if self.first_action is not None:
                print('Call first action')
                self.first_action(self)
            if self.second_action is not None:
                print('Call second action')
                self.second_action(self)    


watcher = Watcher(watch_file, first_action(), second_action())

像上面那樣調用first_action()和second_action()但不在 Class 內部。 我知道是因為我沒有看到打印的“調用第一個動作”或“調用第二個動作”我能夠使用以下代碼正確觸發第一個動作：

watch_file = 'my_file.txt'

def first_action():
    print('First action called')

def second_action():
    print('Second action called')

class Watcher():
    def __init__(self, watch_file, first_action=None, *args):
        self._cached_stamp = 0
        self.filename = watch_file
        self.first_action = first_action
        self.args = args

    # Look for changes in 'my_file.txt'
    def look(self):
        stamp = os.stat(self.filename).st_mtime
        if stamp != self._cached_stamp:
            self._cached_stamp = stamp
            # File has changed, so do something...
            print('File changed')
            if self.first_action is not None:
                print('Call first action')
                self.first_action(*self.args)    


watcher = Watcher(watch_file, first_action)

出於某種原因，我需要為 function 指定*args ，它在調用時不接受任何參數。 有人可以解釋為什么必須使用*args嗎？

Answer 1

您在 init 中做對了，但不是在“Watcher”的調用中。 要傳遞 function 本身，而不是它的返回值，您必須刪除大括號。

watcher = Watcher(watch_file, first_action, second_action)

你應該沒事。