Hack to implement a confirm_button in Streamlit v0.35

confirm_button_hack.py

"""
THIS HAS BEEN DEPRECATED!

We propose you use st.form() instead:

https://blog.streamlit.io/introducing-submit-button-and-forms/
"""

import streamlit as st
import collections
import functools
import inspect
import textwrap

def cache_on_button_press(label, **cache_kwargs):
    """Function decorator to memoize function executions.

    Parameters
    ----------
    label : str
        The label for the button to display prior to running the cached funnction.
    cache_kwargs : Dict[Any, Any]
        Additional parameters (such as show_spinner) to pass into the underlying @st.cache decorator.

    Example
    -------
    This show how you could write a username/password tester:

    >>> @cache_on_button_press('Authenticate')
    ... def authenticate(username, password):
    ...     return username == "buddha" and password == "s4msara"
    ...
    ... username = st.text_input('username')
    ... password = st.text_input('password')
    ...
    ... if authenticate(username, password):
    ...     st.success('Logged in.')
    ... else:
    ...     st.error('Incorrect username or password')
    """
    internal_cache_kwargs = dict(cache_kwargs)
    internal_cache_kwargs['allow_output_mutation'] = True
    internal_cache_kwargs['show_spinner'] = False
    
    def function_decorator(func):
        @functools.wraps(func)
        def wrapped_func(*args, **kwargs):
            @st.cache(**internal_cache_kwargs)
            def get_cache_entry(func, args, kwargs):
                class ButtonCacheEntry:
                    def __init__(self):
                        self.evaluated = False
                        self.return_value = None
                    def evaluate(self):
                        self.evaluated = True
                        self.return_value = func(*args, **kwargs)
                return ButtonCacheEntry()
            cache_entry = get_cache_entry(func, args, kwargs)
            if not cache_entry.evaluated:
                if st.button(label):
                    cache_entry.evaluate()
                else:
                    raise st.ScriptRunner.StopException
            return cache_entry.return_value
        return wrapped_func
    return function_decorator

def confirm_button_example():
    @cache_on_button_press('Authenticate')
    def authenticate(username, password):
        return username == "buddha" and password == "s4msara"

    username = st.text_input('username')
    password = st.text_input('password')

    if authenticate(username, password):
        st.success('You are authenticated!')
        st.write(st.slider('Test widget'))
    else:
        st.error('The username or password you have entered is invalid.')

def display_func_source(func):
    code = inspect.getsource(confirm_button_example)
    code = '\n'.join(code.splitlines()[1:]) # remove first line
    st.code(textwrap.dedent(code))

if __name__ == '__main__':
    st.write("""
        This example shows a hack to create a "confirm button" in Streamlit, e.g.
        to authenticate a username / password pair.
        The correct answer is `buddha` / `s4msara`.
    """)
    display_func_source(confirm_button_example)
    confirm_button_example()

Right now this is not possible without using session_state which is experimental.

(Also, if you are using Streamlit for Teams, we are coming out with a viewer auth feature which will be vastly more elegant than this. @astrojams1 has more details on when this is coming out.)

Thanks for this - wondering why it is not included in streamlit itself?

@nicholas-mitchell:

If you're talking about the confirm button specifically, this has been superseded by st.form which we just released.

If you're talking about session state more generally, it's coming in the next few months! We're working hard on it! 🎈