How can i remove an value in a list

Question

class List:
    def __init__(self, list):
        self.list = list
    
    def delete(self, index):
        if self.list.index(index) in self.list:
            self.list.pop(index)
        else:
          print("The value isn't in the list.")`


list = List(["green", "blue", "yellow", "brown"])


list.delete("no")

I tried to delete the value "no" in the list, and it gives me a Value Error, that says "The value is not in list"

What did you expect to happen? "no" isn't in the list. (Also, naming a variable `list` is a bad idea!) — Samwise, Aug 25 '22 at 03:56
I don't think OP was asking how to remove an element by value (the reason to previously close it), but how to change the behaviour of the existing `.remove()` to print a message when an item cannot be remove by value (as it doesn't exist in the list), so I voted to reopen - accepted answer below. — Grismar, Aug 25 '22 at 22:33

Grismar · Accepted Answer · 2022-08-25T04:20:35.377

Your code has two logic problems:

self.list.index(index) in self.list doesn't do what you think it does, the index won't be in the list, the word may be
self.list.pop(index) would pop index, but it expects an actual index, which is not what you're passing to the method

Your code also suffers from horrible naming. To make a point, here's an almost working version of your code with your naming scheme dialed to 11:

class List:
    def __init__(List, list):
        List.list = list

    def List(List, index):
        if List.list.index(index) > -1:
            List.list.pop(List.list.index(index))
        else:
            print("The value isn't in the list.")


list = List(["list", "List", "LIST", "list "])
list.List("list")
print(list.list)
list.List("not in list")

Output:

['List', 'LIST', 'list ']
Traceback (most recent call last):
  File "F:\Project\Python\sandbox_310\my_list.py", line 15, in <module>
    list.List("not in list")
  File "F:\Project\Python\sandbox_310\my_list.py", line 6, in List
    if List.list.index(index) > -1:
ValueError: 'not in list' is not in list

Here's a more reasonably named version, that catches the exception, so it works as you expect:

class MyList:
    def __init__(self, xs):
        self.xs = xs

    def delete(self, x):
        try:
            self.xs.pop(self.xs.index(x))
        except ValueError:
            print("The value isn't in the list.")


example = MyList(["green", "blue", "yellow", "brown"])
example.delete("green")
print(example.xs)
example.delete("no")

Output;

['blue', 'yellow', 'brown']
The value isn't in the list.

And here's a streamlined version, which no longer throws an exception (because it checks whether it can remove before trying to do so, and not calling .index() which causes the error as well):

class MyList:
    def __init__(self, xs):
        self.xs = xs

    def delete(self, x):
        if x in self.xs:
            self.xs.remove(x)
        else:
            print("The value isn't in the list.")


example = MyList(["green", "blue", "yellow", "brown"])
example.delete("green")
print(example.xs)
example.delete("no")

Of course, you could also just:

class MyList(list):
    def safe_remove(self, x):
        if x in self:
            self.remove(x)
        else:
            print("The value isn't in the list.")

example = MyList(["green", "blue", "yellow", "brown"])
example.remove("green")  # MyList *is* a list, so all standard methods work
print(example)
example.safe_remove("no")  # but using the added safe_remove, you get what you want

Result:

['blue', 'yellow', 'brown']
The value isn't in the list.

score 0 · Answer 2 · answered Aug 25 '22 at 04:42

Firstly, the value ins't in the list.

Secondly, if you want the value "no" from the list the do the following

class List:
def __init__(self, list):
    self.list = list

def delete(self, index):
    if index in self.list:
        self.list.remove(index)
    else:
      print("The value isn't in the list.")

Run below

list = List(["green", "blue", "yellow", "brown", "no"]) --> Create

print(list.list) --> Print your above list

list.delete("no") --> Delete an item

print(list.list) --> re-print the list

How can i remove an value in a list

2 Answers2