Set default value for selectbox

🎈 Using Streamlit
1

Hello everyone,
I am new to streamlit.
I tried to set a default value for sidebar.selectbox.
The code is below.
I appreciate the help!
Thank you in advance.

st.sidebar.header('Settings')

fichier = st.sidebar.selectbox('Dataset', ('djia', 'msci', 'nyse_n', 'nyse_o', 'sp500', 'tse'))

window_ANTICOR = st.sidebar.selectbox('Window ANTICOR', ['<select>',3, 5, 10, 15, 20, 30])
if window_ANTICOR == '<select>':    
    window_ANTICOR == 30

window_OLMAR = st.sidebar.selectbox('Window OLMAR', ['<select>',3, 5, 10, 15, 20, 30])
if window_OLMAR == '<select>':    
    window_OLMAR == 5

eps_OLMAR = st.sidebar.selectbox('Eps OLMAR', ['<select>', 3, 5, 10, 15, 20, 30])
if eps_OLMAR == '<select>':    
    eps_OLMAR == 10

eps_PAMR = st.sidebar.selectbox('Eps PAMR', ['<select>',0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1])
if eps_PAMR == '<select>':    
    eps_PAMR == 0.5

variant = st.sidebar.selectbox('Variant PAMR', (0, 1, 2))
if variant == '<select>':    
    eps_PAMR == 0