Comments (8)
Asaurus1
commented on May 8, 2024
2
@nathancooperjones this is unfortunately less of a "bug" and more an intended but unexpected consequence of the way the streamlit execution model and widget system works. Any time you change the input value of an argument to a widget, streamlit sort of perceived that widget as an entirely new widget, and doesn't guarantee that the old widget value will carry over. There are a couple of technical reasons why it has to be this way, but that's partly what's causing the problem here. There's a "careful dance of information" (for lack of a better term) going on between the frontend webpage and the python backend each run and "new" widgets are treated slightly differently from ones that existed during the last script run. See https://docs.streamlit.io/develop/concepts/architecture/widget-behavior for a little more info.
The other issue I see here is that you're modifying the order of the list after the widget is rendered, which means it doesn't take effect until the next time the script reruns.
Try placing your if statement that reorders the list inside a function that is called by st.selectbox on_change and see if you get more reliable results.
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LukasMasuch
commented on May 8, 2024
1
@nathancooperjones thanks for reporting this 👍 I reproduced it here. As @Asaurus1 explained correctly, its a behaviour that's currently expected (-> changing this to a feature request). But we are aware that it is causing trouble in some usecases.
Related issues for other widgets are:
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Asaurus1
commented on May 8, 2024
1
@nathancooperjones hmm, I think that might be a bit overkill. This should be what you want
import streamlit as st
# set up some dummy session state variables
st.session_state.setdefault("options", ['D', 'C', 'B', 'A', 'F', 'E'])
def update_options():
# move the selected option to the front of the list if it is not already
if st.session_state.selected_option != st.session_state.options[0]:
st.session_state.options.remove(st.session_state.selected_option)
st.session_state.options.insert(0, st.session_state.selected_option)
st.selectbox(
label='Select an option',
options=st.session_state.options,
key="selected_option",
on_change=update_options,
)
st.markdown(f'You selected: {st.session_state.selected_option}')Here's what's happening:
- You create the options list in session_state
- You create a selectbox that is tied to the selected_option key
- When the selection changes, the update_options function is run before your script code and updates the list in session state, causing the order to change.
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Asaurus1
commented on May 8, 2024
1
Right, the "key" here is that you give the widget a "key" argument (pun intended) so you can extract the selected value from within the update_options callback. Otherwise that variable doesn't get updated until the next run of the script reaches the selectbox line, which is already too late.
…
On Apr 22, 2024 at 08:33, Nate Jones ***@***.***> wrote:
>
>
> @nathancooperjones hmm, I think that might be a bit overkill. This should be what you want
>
>
OMG this is SO much better than the solution I had, thank you so much!!
I realized that it didn't work for me because I was assigning the output of selectbox to the variable. This does not work:
import streamlit as st # set up some dummy session state variables if 'options' not in st.session_state: st.session_state.options = ['D', 'C', 'B', 'A', 'F', 'E'] def update_options(): # move the selected option to the front of the list if it is not already if st.session_state.selected_option != st.session_state.options[0]: st.session_state.options.remove(st.session_state.selected_option) st.session_state.options.insert(0, st.session_state.selected_option) st.session_state.selected_option = st.selectbox( label='Select an option', options=st.session_state.options, on_change=update_options, ) st.markdown(f'You selected: {st.session_state.selected_option}')
But this does:
import streamlit as st # set up some dummy session state variables if 'options' not in st.session_state: st.session_state.options = ['D', 'C', 'B', 'A', 'F', 'E'] def update_options(): # move the selected option to the front of the list if it is not already if st.session_state.selected_option != st.session_state.options[0]: st.session_state.options.remove(st.session_state.selected_option) st.session_state.options.insert(0, st.session_state.selected_option) st.selectbox( label='Select an option', options=st.session_state.options, key='selected_option', # change here on_change=update_options, ) st.markdown(f'You selected: {st.session_state.selected_option}')
This is super good to know going forward, thank you!!
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github-actions
commented on May 8, 2024
If this issue affects you, please react with a 👍 (thumbs up emoji) to the initial post.
Your feedback helps us prioritize which bugs to investigate and address first.
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ameen7626
commented on May 8, 2024
is there any workaround to fix this issue
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nathancooperjones
commented on May 8, 2024
@Asaurus1 @LukasMasuch thanks for the reply and linking some similar issues, I appreciate the response! I tried moving the option sorting logic into a function called by the selectbox's on_change but the issue still happens :(
As a workaround in the meantime, I've been caching the options sent into the selectbox so the widget doesn't reset each time until the set of options actually change. It's a SUPER hacky, but it works well-enough for my use case:
import streamlit as st
# set up some dummy session state variables
if 'options' not in st.session_state:
st.session_state.options = ['D', 'C', 'B', 'A', 'F', 'E']
# cache the options to the ``st.selectbox`` doesn't reset and ignore a user's input if the order of
# the options changes
if set(st.session_state.get('_cached_options', [])) != set(st.session_state.options):
st.session_state._cached_options = sorted(st.session_state.options)
if 'selected_option' in st.session_state:
st.session_state._selectbox_index = (
st.session_state._cached_options.index(st.session_state.selected_option)
)
else:
st.session_state._selectbox_index = 0
st.session_state.selected_option = st.selectbox(
label='Select an option',
options=st.session_state._cached_options,
index=st.session_state._selectbox_index,
)
st.markdown(f'You selected: {st.session_state.selected_option}')
# move the selected option to the front of the list if it is not already
if st.session_state.selected_option != st.session_state.options[0]:
st.session_state.options.remove(st.session_state.selected_option)
st.session_state.options.insert(0, st.session_state.selected_option)
# dummy logic to add an option just to see how ``st.session_state.options`` changes
if st.button('Add an option'):
option_to_add = 1
while True:
if str(option_to_add) not in st.session_state.options:
st.session_state.options.append(str(option_to_add))
st.rerun()
option_to_add += 1
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nathancooperjones
commented on May 8, 2024
@nathancooperjones hmm, I think that might be a bit overkill. This should be what you want
OMG this is SO much better than the solution I had, thank you so much!!
I realized that it didn't work for me because I was assigning the output of selectbox to the variable. This does not work:
import streamlit as st
# set up some dummy session state variables
if 'options' not in st.session_state:
st.session_state.options = ['D', 'C', 'B', 'A', 'F', 'E']
def update_options():
# move the selected option to the front of the list if it is not already
if st.session_state.selected_option != st.session_state.options[0]:
st.session_state.options.remove(st.session_state.selected_option)
st.session_state.options.insert(0, st.session_state.selected_option)
st.session_state.selected_option = st.selectbox(
label='Select an option',
options=st.session_state.options,
on_change=update_options,
)
st.markdown(f'You selected: {st.session_state.selected_option}')But this does:
import streamlit as st
# set up some dummy session state variables
if 'options' not in st.session_state:
st.session_state.options = ['D', 'C', 'B', 'A', 'F', 'E']
def update_options():
# move the selected option to the front of the list if it is not already
if st.session_state.selected_option != st.session_state.options[0]:
st.session_state.options.remove(st.session_state.selected_option)
st.session_state.options.insert(0, st.session_state.selected_option)
st.selectbox(
label='Select an option',
options=st.session_state.options,
key='selected_option', # change here
on_change=update_options,
)
st.markdown(f'You selected: {st.session_state.selected_option}')This is super good to know going forward, thank you!!
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