Unable to update st.file_uploader with a new file

Using Streamlit
, ,
1

I am writing a script that will update the contents of a variable when a new file uploaded using st.file_uploader(). I am trying to achieve this using the ‘on_change’ function and accessing the new value via the key_field. However, after the first file is successfully uploaded, when I upload a second file, I instead get an error “‘NoneType’ object has no attribute ‘read’”

Below is my code:

def load_new_file():
    with st.spinner("Please wait.. loading the file"):
        new_file = st.session_state["new_file"]
        bytes_data = new_file.read()
        upload_file_to_blob(STORAGE_CONNECTION_STRING, STORAGE_CONTAINER_NAME, "app_data/"+new_file.name, bytes_data)
        st.session_state.document_url = get_blob_sas_url(STORAGE_CONNECTION_STRING, STORAGE_CONTAINER_NAME, "app_data/"+new_file.name)
    return 

st.session_state.uploaded_file = st.file_uploader("Choose the PDF file", accept_multiple_files=False, key="new_file", on_change=load_new_file)

I get this error on the line " bytes_data = new_file.read()" everytime I upload a second file and the callback function gets triggered. This doesn’t happen when I upload the file for the first time though. Any idea what could be causing the issue?

I am running the code locally on a Python 3.9 environment with streamlit version 1.28.2

2

Uploading a new file actually triggers the callback twice:

  1. The first time, the value in session state will be None.
  2. The second time, the value in session state will be the newly uploaded file.
3

Ah this makes sense. Thanks for clarifying! Do you have any suggestions for how I could solve this issue?

4

Detect whether new_file is None or not, decide what to do in each case. You don’t want to call new_file.read() when new_file is None.

1 Like
5

Yes, got it working. Thank you!!

6

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