how to check non-empty selection?-CodePudding

I am using plotly-dash dropdown menu with multiple selection enabled. so the dropdown menu returned either an empty list when no selection, or a string ( with one selection) or list of strings ( with multiple selection).

How do I check if returned is not empty?

if I use below, it doesn't work for empty list


if selection is not None:

Thanks for your help.

CodePudding user response：

I think this should work:

def check_selection(selection):
    if selection:
        if isinstance(selection, list):
            return "Multiple Selections"
        else:
            return "One Selection"
    else:
        return "No Selection"

Empty sequences (like strings and lists) are considered "falsy" in Python, and evaluate to the boolean False. Please let me know if I interpreted your question correctly, and this answer helps.

CodePudding user response：

Empty list is not same as None. You can check length of the list using len() function. If length is 0, the list is empty.

Try it:

if len(selection) == 0:
    #code if the list is empty
else:
    #code if list is not empty

The code will also work for string, because as per question if single selection is made, the menu will return a string(which will have some length). We can check in else part of the code as if it is a string or list using type() function.

rlist = [1, 2, 3]
rstring = 'test'
def test_selection(obj):
    if len(obj) == 0:
        print('empty')
    else:
        if type(obj) is str:
            print('str object')
        else:
            print('list')

test_selection(rlist) #output :- list
test_selection(rstring) #output :-  str object
test_selection([])  #output :-  empty