Change the state of an item from code?

Using Streamlit
,
1

Hi all.

Can I change the state of an item from code? Suppose I have a radio button option. Now, further down in my logic code I want to reset the selection to a certain value as a result of a computation since the outcome determines that a certain option must be selected (i.e. computation is not valid for a certain setting)…

Is this possible? How can I access an existing radio button widget and set it to a certain value by code…?

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2

Hey @cwerner, welcome to the forums! :tada:

Depending on your needings, you could solve that in many ways:

  1. Using an empty element
  2. Using st.cache()
  3. Using “Session State” as shown here

Please let us know if this helps you

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3

Thanks for the pointers @arraydude

However, given your links I do not see how I would write code to set an existing radio button to a new value depending on some outcome from a calculation?

Sorry if I miss the obvious?

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4

Hi @cwerner,

Here’s an example snippet using st.empty()

import streamlit as st
import time

options = ("male", "female")

a = st.empty()

value = a.radio("gender", options, 0)

st.write(value)

time.sleep(2)

value = a.radio("gender", options, 1)

st.write(value)
5

Thanks for the example!

Did not know about st.empty(). What’s the exact purpose in this scenario?

Also, I can change the value via code, but the radio button itself does not change… Is this only on my install?

Cheers

6

I’m not sure what you mean exactly but this is what I understood:

value = st.radio(“choices”, [“choice1”, “choice2”, “choice3”, “choice4”])
#the user select an option

#some computations here that change value to whatever you want

you could use session_state like this
value = SessionState.get(val = “”)
value.val = st.radio(“choices”, [“choice1”, “choice2”, “choice3”, “choice4”])

#and later change it how ever you want like this
value.val = “something here”

7

I got the result value changed, but expected the radio button to “jump” to my intended selection (which does not happen)…

Scenario: I have an option that is not yet implemented and when ever it’s selected it should emit a warning and jump to the valid option…

Did not check session state yet… will have a go with this…

8

I got you this work around, but it’s a little bit messy. I hope someone comes with a better solution.
Here’s an example

import streamlit as st
from session_state import SessionState

session_state = SessionState.get(hist = [], val = "", index=0, radio_key=0)

st.header("testing")

x = st.empty()

class params():
    def __init__(self, session_state):
        self.radio_key_str = str(session_state.radio_key)
        self.index = session_state.index
        self.val = x.radio("options",["paris", "milan", "NY"], self.index, key=self.radio_key_str)

    def reset(self):
        self.__init__(session_state)

    def update_session(self, session_state):
        session_state.val = self.val
        session_state.index = self.index
        session_state.radio_key = session_state.radio_key+1
        x.empty()
        self.reset()


params = params(session_state)


st.write(params.index)
st.write(params.val)

if st.button("set to default"):
    params.index = 1
    params.update_session(session_state)
    st.write(params.index)
    st.write(params.val)

st.write("end")
9

Hi @cwerner,

I’m seeing the radio input selection visually jump to the new option.

See video at https://youtu.be/kkW7-PBJ0m8

Please post a video along with your code snippet and OS version, browser version, python version, etc… if you’re not seeing the same.

st.empty is used to get a placeholder that you can reference later, to fill it with an element/widget.
See docs at https://streamlit.io/docs/api.html#streamlit.empty

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10

Thanks Jonathan for the video and reply.

I’m not quite sure. I think when I last tried it I was in a python 3.8 env. I now tried it within my current project env and now it jumps…?!?

However, I’m not sure the 2nd st.write(value) work as intended?

I modified my example slightly. This now work 95%, however there’s a small detail I’d like to change.

import streamlit as st
import time

options = ("male", "female")

a = st.empty()

value = a.radio("gender", options, 0, key='a')

if value == 'male':
    st.write(value)
elif value == 'female':
    st.write(value)
    time.sleep(1)
    a.radio("gender", options, 0, key='b')
    st.write(value)     # this produces a second line, 
                        # ideally it should replace the 
                        # previous st.write output...
11

Hi @cwerner,

See the following example which you can mimic to get your desired solution.

12

Thanks, will check it out :+1:

13

Hey @cwerner & @Soufiane_Fartit ,

Have some updates regarding Session State! It’s now natively supported in Streamlit via the 0.84.0 release! :partying_face:

Here are some helpful links:

Looking forward to hearing what you think :balloon:

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