如何使用Python从值列表中删除特定值

Question

I am trying to remove the particular value from the list of key. I got Type error. I wrote function to add and remove the key. need to remove a particular value from the key

class my_dict(dict):    
    def add(self, key, value):
        self.setdefault(key, []).append(value)

    def remove_key(self, key):
        del self[key]

    #Error part
    def remove_value(self,key,value):
        for value in dict.values():
            if v in value:
                value.remove(v)

dict_obj = my_dict()
dict_obj.add('key1', 'value1')
dict_obj.add('key2', 'value2')
dict_obj.add('key1', 'value3')
print(dict_obj)  

>>{'key1': ['value1', 'value3'], 'key2': ['value2']}


dict_obj.remove_value('key1','value3')
print(dict_obj)  

My Out

TypeError: descriptor 'values' of 'dict' object needs an argument

Desired Output

>>{'key1': ['value1'], 'key2': ['value2']}

Answer 1

You've got a couple problems in:

def remove_value(self,key,value):
    for value in dict.values():
        if v in value:
            value.remove(v)

1. You used dict.values() , not self.values() ; the former is trying to call dict.values with no dict instance to operate on
2. You named two things value , and one replaces the other (while using v without ever naming anything v )

Minimal fix would be:

def remove_value(self,key,v):  # Name argument v to match test and remove
    for value in self.values():  # Call values on self
        if v in value:
            value.remove(v)

Slightly more readable fix (that would also limit removal to the specified key , which I'm guessing was the intent, since you receive a key argument) would be:

def remove_value(self, key, toremove):
    try:
        self[key].remove(toremove)
    except (KeyError, ValueError):
        pass
    else:
        if not self[key]:
            del self[key]

Remove the try / except block if you want non-existent keys or values to raise KeyError or ValueError respectively. Remove the else block if you want to leave a key in place even if all values are removed.

Answer 2

you need to remove it from self[key].value if value in self[key] :

def remove_value(self,key,value):
    if value in self.get(key, []):
        self[key].remove(value)

But similar to your previous related question , this seems like you'd be better suited using defaultdict than trying to monkeypatch your own dict-like object.

from collections import defaultdict
mydict = defaultdict(list)
mydict['key1'].append('value1')
mydict['key1'].append('value3')
mydict['key2'].append('value2')
if 'value3' in mydict['key1']:
    mydict['key1'].remove('value3')