Component state management example

state_management.py

import streamlit as st #pip install streamlit
import yaml #pip install pyyaml

from streamlit_ace import st_ace #to install: pip install streamlit_ace

#allow user to edit config file in yaml format. Add couple checks below
with st.expander('example', expanded=True):
    st.markdown("""
    for this example, yaml must define at least a sample_list member. As the example below:  
    ```yaml 
    sample_list:  
        - item 1  
        - item 2  
        - item 3  
    ```
    If key is not fixed, component will sometime reset between refreshs, causing bad user experience.
    if key is fixed component state will be held between refreshs... to reset the component, one must change the key.
    """)
fix_key = st.checkbox("Fix component key")

content = st_ace(
    auto_update=True,
    placeholder="Edit yaml", 
    language="yaml",
    show_gutter=True,
    value = st.session_state.get('content', ''),
    theme='dawn',
    key=None if not fix_key else 'fixed_key', 
    height=400
    )
try:
    yaml_content = yaml.load(content, yaml.Loader)

    #Some basic validation of configuration just for post-processing example
    if ('sample_list' not in yaml_content):
        raise ValueError('file must define at least a **sample_list:** key')

    if not yaml_content['sample_list']:
        raise ValueError('sample_list list is empty!')

    st.session_state['content'] = content

    #if is valid yaml allows user to save file back to disk
    st.download_button("Download yaml", data=content, file_name="config.yaml")
except ValueError as ex:
    st.error(ex)
except:
    st.error("Bad YAML syntax")