Batch elements and input widgets with st.form

Let's take a look at how to use st.form to batch elements and input widgets.

In Streamlit, every widget interaction causes a rerun of the app. However, there are times when you might want to interact with a couple of widgets and submit those interactions while triggering a single re-run of the app.

Using st.form you can batch input widgets together and along with st.form_submit_button submit the state inside these widgets with the click of a single button.

# Forms can be declared using the 'with' syntax
with st.form(key='my_form'):
    text_input = st.text_input(label='Enter your name')
    submit_button = st.form_submit_button(label='Submit')

# Alternative syntax, declare a form and use the returned object
form = st.form(key='my_form')
form.text_input(label='Enter some text')
submit_button = form.form_submit_button(label='Submit')

# st.form_submit_button returns True upon form submit
if submit_button:
    st.write(f'hello {name}')

Forms can appear anywhere in your app (sidebar, columns etc), but there are some constraints:

• A form cannot have interdependent widgets, i.e. the output of widget1 cannot be the input to widget2 inside a form.
• By design, interacting with widgets inside st.form does not trigger a re-run. Because of this reason, st.button cannot be declared inside st.form.
• st.form cannot be embedded inside another st.form.
• Forms must have an associated st.form_submit_button. Clicking this button triggers a re-run. Streamlit throws an error if a form does not have an associated st.form_submit_button.