Dat_input stores function instead of value into session state

Using Streamlit
1

Summary

date_input widget stores the datetime function into session state instead of value

Steps to reproduce

Code snippet:

with st.form("add_user", clear_on_submit=False):
  firstName = st.text_input("Vorname", key='firstName')
  lastName = st.text_input("Nachname", key='lastName')

  birthDate = st.date_input("Birthday", min_value=datetime.date(1910, 2, 1), format='DD/MM/YYYY', key='birthDate')
 submitted = st.form_submit_button("Save")
 if submitted:
   def add_user():

new_user = { 'firstName' : st.session_state['firstName'],
                 'lastName' : st.session_state['lastName'],
                 'birthDate' : str(st.session_state['birthDate']),
                 'entryDate' : st.session_state['entryDate'],
                 }
  return new_user

st.write(add_user())

generates
{
“firstName”:“some first name”
“lastName”: “some last name”
“birthDate”:“2023-09-22”
“entryDate”:“datetime.date(2023, 9, 22)”
}

Expected behavior:

Value is stored in the session state - i.e. 2023-09-22 or document the representation of the data

Actual behavior:

Datetime function as string

2

Hi @mauermbq ,

You can use iso format for that. The input_date is returning a string but your entry date update is returning the date function. See my example,

from datetime import date, datetime

with st.form("add_user", clear_on_submit=False):
    firstName = st.text_input("Vorname", key="firstName")
    lastName = st.text_input("Nachname", key="lastName")

    birthDate = st.date_input(
        "Birthday",
        min_value=date(1910, 2, 1),
        # format="DD/MM/YYYY",
        key="birthDate",
    )

    submitted = st.form_submit_button("Save")
    if submitted:

        def add_user():
            new_user = {
                "firstName": st.session_state["firstName"],
                "lastName": st.session_state["lastName"],
                "birthDate": str(st.session_state["birthDate"]),
                "entryDate": datetime.now().date().isoformat(),
            }
            return new_user

        st.write(add_user())
3

After fixing the indentation, clicking Save raises a KeyError. Looks like you forgot to post the code where you assign a value to st.session_state["entryDate"].

4

…sorry this was copy/paste error, my original code is more complex.

However, that st.write renders correct and that extracting the same session object to a dict returns something completely different was confusing. It would be helpful in the doc explaining what python object is returning exactly, and what happens under the hood during rendering.

so
birthDate = st.date_input(“Birthday”, min_value=datetime.date(1910, 2, 1), format=‘DD/MM/YYYY’, key=‘birthDate’)

when entering 02/10/1987 you get:

st.write(st.session_state[‘birthDate’]) → Output for example 02-10-1987 (as expected)

new_user = { ‘birthDate’: st.session_state[‘birthDate’])} → {‘birthDate’: “datetime.date(1987, 10, 02)”}
(that’s really unexpected)

5

That is because st.write actually calls st.json when passed a dictionary, then st.json serializes its argument as JSON. Instances of datetime.date are serialized to their string representation using repr (not str), which is what you are seeing.