I would like to better understand the logic behind session_state because I am in trouble. I noticed that if I put a dictionary in session_state, let’s say mem, then I delete a key directly, for example:
del st.session_state.mem[‘ingr’]
if I enter the same key again through a widget, the previous value associated with that key reappears again, despite having deleted it before.
How do you permanently delete a value in a data structure stored in session_state?
Thanks for opening this issue.
if I enter the same key again through a widget, the previous value associated with that key reappears again, despite having deleted it before.
Can you share a minimal code example so that I can reproduce the problem?
Thanks,
Abhi
it’s not exactly an easy code to follow. Basically the user enters a recipe in the form of a dictionary in which each ingredient corresponds to a value. The user must be able to go back to the recipe, add, remove and change values.
################ FUNCTION ################
def changed_ingr():
if st.session_state.ricetta_memoria_changed:
if len(st.session_state.ricetta_memoria_changed)>len(st.session_state.ricetta_memoria[1]):
ingr=set(st.session_state.ricetta_memoria_changed)-set(list(st.session_state.ricetta_memoria[1].keys()))
ingr=list(ingr)[0]
st.session_state.ricetta_memoria[1][ingr]=0.0
elif len(st.session_state.ricetta_memoria_changed)<len(st.session_state.ricetta_memoria[1]):
ingr=set(list(st.session_state.ricetta_memoria[1].keys()))-set(st.session_state.ricetta_memoria_changed)
ingr=list(ingr)[0]
del st.session_state.ricetta_memoria[1][ingr] # fai l'update della ricetta in memoria
################### MAIN ##################
if "ricetta_memoria" not in st.session_state:
st.session_state.ricetta_memoria = ["",ricetta,dati_temp_immessi]
select=st.multiselect('Scegli gli ingredienti della tua ricetta',df.index.tolist(),on_change=changed_ingr,
default=list(st.session_state.ricetta_memoria[1].keys()), key="ricetta_memoria_changed")
for key in list(st.session_state.ricetta_memoria[1].keys()):
st.session_state.ricetta_memoria[1][key]=st.number_input(key,min_value=0.,
value=st.session_state.ricetta_memoria[1][key])For reference, every widget with a key is automatically added to Session State. Please see our docs:
https://docs.streamlit.io/en/stable/session_state_api.html#session-state-and-widget-state-association
I made some assumptions about inputs to be able to run your code. The code below allows me to add, remove and update ingredients
import streamlit as st
ricetta = {
'rice': 3.0,
'cheese': 5.0
}
dati_temp_immessi = 'x'
def changed_ingr():
if st.session_state.ricetta_memoria_changed:
if len(st.session_state.ricetta_memoria_changed) > len(st.session_state.ricetta_memoria[1]):
ingr = set(st.session_state.ricetta_memoria_changed) - set(list(st.session_state.ricetta_memoria[1].keys()))
ingr = list(ingr)[0]
st.session_state.ricetta_memoria[1][ingr] = 0.0
elif len(st.session_state.ricetta_memoria_changed) < len(st.session_state.ricetta_memoria[1]):
ingr = set(list(st.session_state.ricetta_memoria[1].keys())) - set(st.session_state.ricetta_memoria_changed)
ingr = list(ingr)[0]
del st.session_state.ricetta_memoria[1][ingr] # fai l'update della ricetta in memoria
if "ricetta_memoria" not in st.session_state:
st.session_state.ricetta_memoria = ["",ricetta,dati_temp_immessi]
select = st.multiselect('Scegli gli ingredienti della tua ricetta',
['rice', 'cheese', 'apples', 'water'],on_change=changed_ingr,
default=list(st.session_state.ricetta_memoria[1].keys()),
key="ricetta_memoria_changed"
)
for key in list(st.session_state.ricetta_memoria[1].keys()):
st.session_state.ricetta_memoria[1][key] = st.number_input(key, min_value=0., value=0.0)
Note that I have a suggestion for a change in the following line in your code
BEFORE
st.session_state.ricetta_memoria[1][key] = st.number_input(key,min_value=0., value=st.session_state.ricetta_memoria[1][key])
The code above can lead to an off by one error. So I would recommend setting value=0.0
AFTER
st.session_state.ricetta_memoria[1][key] = st.number_input(key,min_value=0.,value=0.0)
thank you for your reply Abhi, but your code doesn’t preserve state (ingredients and values):
import streamlit as st
my_page = st.sidebar.radio(‘Section’, [‘Recipe’,‘Other’])
if my_page == ‘Recipe’:
ricetta = {
'rice': 3.0,
'cheese': 5.0
}
dati_temp_immessi = 'x'
def changed_ingr():
if st.session_state.ricetta_memoria_changed:
if len(st.session_state.ricetta_memoria_changed) > len(st.session_state.ricetta_memoria[1]):
ingr = set(st.session_state.ricetta_memoria_changed) - set(list(st.session_state.ricetta_memoria[1].keys()))
ingr = list(ingr)[0]
st.session_state.ricetta_memoria[1][ingr] = 0.0
elif len(st.session_state.ricetta_memoria_changed) < len(st.session_state.ricetta_memoria[1]):
ingr = set(list(st.session_state.ricetta_memoria[1].keys())) - set(st.session_state.ricetta_memoria_changed)
ingr = list(ingr)[0]
del st.session_state.ricetta_memoria[1][ingr]
if "ricetta_memoria" not in st.session_state:
st.session_state.ricetta_memoria = ["",ricetta,dati_temp_immessi]
select = st.multiselect('Scegli gli ingredienti della tua ricetta',
['rice', 'cheese', 'apples', 'water'],on_change=changed_ingr,
default=list(st.session_state.ricetta_memoria[1].keys()),
key="ricetta_memoria_changed"
)
for key in list(st.session_state.ricetta_memoria[1].keys()):
st.session_state.ricetta_memoria[1][key] = st.number_input(key, min_value=0., value=0.0)
else:
st.write("another section")
@Fabio_Pasquarella : To be more precise, do you mean that toggling between Recipe and Other doesn’t preserve the state of the number_input widgets?
yes @abhi, I need to preserve the whole recipe (ingredients and values)
I see, in that case you can consider adding a callback to update the value of ingredients as follows:
def update_value(key):
st.session_state.ricetta_memoria[1][key] = st.session_state[key]
for key in list(st.session_state.ricetta_memoria[1].keys()):
st.number_input(key, min_value=0.,
value=st.session_state.ricetta_memoria[1][key], key=key,
on_change=update_value, args=(key,)
)
@abhi thank you very much for your time!
@Fabio_Pasquarella : Happy to help 