Python – Streamlit (Part III)

By | 19/03/2025
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Python – Streamlit (Part I)
Python – Streamlit (Part II)

In this last post on Streamlit, we will see how to manage a form Data, how to manage Buttons and Events and finally we will see how to manage the Session State.

FORM
Forms in Streamlit allow us to group multiple input widgets and submit them together, making it easier to manage related data.
Let’s create a detailed form that incorporates various Streamlit widgets like sliders, date pickers, multi-selects, checkboxes, and radio buttons, along with validation checks:

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import streamlit as st
 
# Create a form
with st.form(key='detailed_form'):
    # Text input
    name = st.text_input("Enter your name")
 
    # Check if name is empty
    if name.strip() == "":
        st.error("Name cannot be empty")
 
    # Number input
    age = st.number_input("Enter your age", min_value=0, max_value=120, step=1)
     
    # Validate age
    if age < 18:
        st.warning("Age must be 18 or above")
 
    # Slider input
    satisfaction = st.slider("Rate your satisfaction (1-10)", min_value=1, max_value=10, value=5)
 
    # Date input
    birth_date = st.date_input("Select your birth date")
 
    # Validate date
    from datetime import date
    if birth_date > date.today():
        st.error("Birth date cannot be in the future")
 
    # Multi-select input
    skills = st.multiselect("Select your skills", ["Python", "R", "SQL", "Machine Learning", "Data Visualization"])
 
    # Ensure at least one skill is selected
    if not skills:
        st.warning("Please select at least one skill")
 
    # Checkbox input
    agree = st.checkbox("I agree to the terms and conditions")
 
    # Radio button input
    gender = st.radio("Select your gender", ["Male", "Female", "Other"])
 
    # Submit button
    submitted = st.form_submit_button("Submit")
 
# Handle form submission
if submitted:
    if agree:
        st.success(f"Thank you, {name}! Here is the information you submitted:")
        st.write(f"Age: {age}")
        st.write(f"Satisfaction Level: {satisfaction}")
        st.write(f"Birth Date: {birth_date}")
        st.write(f"Skills: {', '.join(skills)}")
        st.write(f"Gender: {gender}")
    else:
        st.error("You must agree to the terms and conditions to submit the form.")


BUTTON AND EVENTS
Buttons are a core interactive component in Streamlit, and they can trigger specific actions or events:

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import streamlit as st
  
# Initialize session state for dynamic message
if "dynamic_message" not in st.session_state:
    st.session_state.dynamic_message = ""
  
# Define button actions
def set_message(text):
    st.session_state.dynamic_message = text
  
# Buttons
st.button("Say Hello", on_click=set_message, args=("Hello!",))
st.button("Say Goodbye", on_click=set_message, args=("Goodbye!",))
  
# Display dynamic message
st.write(st.session_state.dynamic_message)

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import streamlit as st
 
# Toggle a boolean state
if "toggle" not in st.session_state:
    st.session_state.toggle = False
 
if st.button("Toggle State"):
    st.session_state.toggle = not st.session_state.toggle
 
st.write(f"Current State: {'On' if st.session_state.toggle else 'Off'}")


SESSION STATE
Session state allows us to store and manipulate data across user interactions and app reruns:

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import streamlit as st
 
# Initialize session state for counter
if "counter" not in st.session_state:
    st.session_state.counter = 0
 
# Increment and Decrement Buttons
col1, col2 = st.columns(2)
 
with col1:
    if st.button("Increment"):
        st.session_state.counter += 1
 
with col2:
    if st.button("Decrement"):
        st.session_state.counter -= 1
 
st.write(f"Counter Value: {st.session_state.counter}")

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import streamlit as st
 
# Initialize session state variables
if "resettable_data" not in st.session_state:
    st.session_state.resettable_data = "Initial Data"
 
# Function to update the state and force a rerun
def update_data():
    st.session_state.resettable_data = "Updated Data"
 
def reset_data():
    st.session_state.resettable_data = "Initial Data"
 
# Display current state
st.write(f"Data: {st.session_state.resettable_data}")
 
# Buttons with actions
st.button("Update Data", on_click=update_data)
st.button("Reset Data", on_click=reset_data)




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