How to raise error if user tries to enter duplicate entries in a set in Python?

Question

I tried to enter 5 similar elements in a set and print it at last. It took all the elements without raising any error but stored only one since all were same. I want to know if it is possible that the moment i input a value which is already present in the set , user is prompted with an error that the value already present in the set. I want to do this with set only , not with list or dict on anything else.

Asked By: sopho-saksham

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Source

Answer 1

You can just check if it exist, then raise an error:

my_set = set()

for i in some_list_of_user_input:
    if i in my_set:
        raise ValueError(f'{i} is already present in the set')
    my_set.add(i)

Answered By: Burhan Khalid

Answer 2

If you want to raise an exception on duplicate insertion, you could do something like this:

class DuplicateKeyError(Exception): pass

class SingleSet(set):
    def add(self, value):
        if value in self:
            raise DuplicateKeyError('Value {!r} already present'.format(value))
        super().add(value)

    def update(self, values):
        error_values = []
        for value in values:
            if value in self:
                error_values.append(value)
        if error_values:
            raise DuplicateKeyError('Value(s) {!r} already present'.format(
                                    error_values))
        super().update(values)

my_set = SingleSet()
value = 'something'
while value:
    value = input('Enter a value: ')
    try:
        my_set.add(value)
    except DuplicateKeyError as e:
        print(e)

Answered By: Wayne Werner

How to raise error if user tries to enter duplicate entries in a set in Python?

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