Function decorator to store singleton objects.
Each singleton object is shared across all users connected to the app. Singleton objects must be thread-safe, because they can be accessed from multiple threads concurrently.
(If thread-safety is an issue, consider using st.session_state to store per-session singleton objects instead.)
You can clear a memoized function's cache with f.clear().
| Function signature | |
|---|---|
st.experimental_singleton(func=None, *, show_spinner=True, suppress_st_warning=False) | |
| Parameters | |
func (callable) | The function that creates the singleton. Streamlit hashes the function's source code. |
show_spinner (boolean) | Enable the spinner. Default is True to show a spinner when there is a "cache miss" and the singleton is being created. |
suppress_st_warning (boolean) | Suppress warnings about calling Streamlit functions from within the singleton function. |
Example
@st.experimental_singleton def get_database_session(url): # Create a database session object that points to the URL. return session s1 = get_database_session(SESSION_URL_1) # Actually executes the function, since this is the first time it was # encountered. s2 = get_database_session(SESSION_URL_1) # Does not execute the function. Instead, returns its previously computed # value. This means that now the connection object in s1 is the same as in s2. s3 = get_database_session(SESSION_URL_2) # This is a different URL, so the function executes.By default, all parameters to a singleton function must be hashable. Any parameter whose name begins with _ will not be hashed. You can use this as an "escape hatch" for parameters that are not hashable:
@st.experimental_singleton def get_database_session(_sessionmaker, url): # Create a database connection object that points to the URL. return connection s1 = get_database_session(create_sessionmaker(), DATA_URL_1) # Actually executes the function, since this is the first time it was # encountered. s2 = get_database_session(create_sessionmaker(), DATA_URL_1) # Does not execute the function. Instead, returns its previously computed # value - even though the _sessionmaker parameter was different # in both calls.A singleton function's cache can be procedurally cleared:
@st.experimental_singleton def get_database_session(_sessionmaker, url): # Create a database connection object that points to the URL. return connection get_database_session.clear() # Clear all cached entries for this function.