有没有办法检查何时将某些内容添加到列表中，例如“a=[]”

Question

I want to print something whenever something is added to a list that I've defined earlier in the code. How do I go about doing this?

a = []

Couldn't find anything on Google about this

Answer 1

There's no built-in way to do this, but you can very easily make your list a user-defined class inheriting from list and hook into the append method:

class MyList(list): 
    def append(self, item): 
        print(f'item {item} will be appended to {str(self)}') 
        return_value = super().append(item) 
        print(f'append succeeded -> list is now {str(self)}') 
        return return_value

mylist = MyList('abc')

print(mylist)
# output:
# ['a', 'b', 'c']

mylist.append('d')
# output:
# item d will be appended to ['a', 'b', 'c']
# append succeeded -> list is now ['a', 'b', 'c', 'd']

print(mylist)
# output:
# ['a', 'b', 'c', 'd']