Session_state - how to use it to save values while navigating through a multi_page app?

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1

“Hello everyone! I’m new to Streamlit and I need some help! In the code below, how can I ensure that the widget variables remain saved, even when navigating through different pages of the app? When I return to the page with the code, the values reset to zero! Can you help me?”

def process_form():
			# Inicializa os valores no st.session_state se eles ainda não existirem
			if 'n_ha' not in st.session_state:
				st.session_state['n_ha'] = 0
			if 'p_ha' not in st.session_state:
				st.session_state['p_ha'] = 0
			if 'k_ha' not in st.session_state:
				st.session_state['k_ha'] = 0
			if 's_ha' not in st.session_state:
				st.session_state['s_ha'] = 0

			# Define o formulário
			with st.form(key='my_form'):
				# Define os widgets dentro do formulário
				n_ha = st.number_input('Digite a quantidade de Nitrogênio (N) por ha:', min_value=0, format='%d', key='n_ha_input', value=st.session_state['n_ha'])
				p_ha = st.number_input('Digite a quantidade de Fósforo (P) por ha:', min_value=0, format='%d', key='p_ha_input', value=st.session_state['p_ha'])
				k_ha = st.number_input('Digite a quantidade de Potássio (K) por ha:', min_value=0, format='%d', key='k_ha_input', value=st.session_state['k_ha'])
				s_ha = st.number_input('Digite a quantidade de Enxofre (S) por ha:', min_value=0, format='%d', key='s_ha_input', value=st.session_state['s_ha'])

				# Adiciona um botão submit ao formulário
				submit_button = st.form_submit_button(label='Simular menores custos')

			# Se o botão submit for pressionado e o formulário for submetido
			if submit_button:
				# Armazena os valores dos widgets no st.session_state
				st.session_state['n_ha'] = n_ha
				st.session_state['p_ha'] = p_ha
				st.session_state['k_ha'] = k_ha
				st.session_state['s_ha'] = s_ha
		process_form()

		# Defina as variáveis globalmente para uso posterior
		n_ha = st.session_state['n_ha']
		p_ha = st.session_state['p_ha']
		k_ha = st.session_state['k_ha']
		s_ha = st.session_state['s_ha']
2

Hi @Marco_Antonio_de_Oli . The following repo will help you that how to manage session for multi pages.
Repo link

3

I’m also trying to figure out how to share the same session data even when I change from page to page. Session data seems to just randomly (but reliably) disappear when I switch to a new page. Without a solution to this Streamlit is basically useless for anything but single pages.

4

Hi,

Yes session state is preserved across pages in a multipage app. This is given that the session state variable should be initialized first then accessed at a later point either on the same page or on another page.

An error may arise if a session state is accessed before it is initialized. Thus, it’s always nice to check the code for this possible sequential initialization prior to use.

Hope this helps!

5

It’s not quite as simple as “yes it just works”. Streamlit definitely has a bug, and this is the thread where I posted my solution:

1 Like
6

There’s quite a number of threads about retaining state across pages. After reading them and the docs (Widget behavior - Streamlit Docs), I ended up running this function at the top of every page:

def retain_session_state(ss):
    state_vars = ss.keys()
    for var in state_vars:
        if var in ss and not var.startswith("FormSubmitter"):
            ss[var] = ss[var]

where ss=st.session_state
to prevent Streamlit from auto-deleting them.
As long as the widgets’ keys are unique across the pages, I don’t think there’s a problem.
Is there any concern to this approach?