Streamlit Python uploaded files

Question

Help.I'm new to a Streamlit and the following code was taken from my app.py. I ran streamlit run app.py so a new browser would popup and displaying Streamlit App.

from be_app import * 

print_heading("Welcome to PDF Merger")
print_text("The purpose of this system is to merge bulk pdf at once.")

print_heading("How does it work?",2)
print_text("Basically the system will read all of your pdf files, then merge them based on their name.")
print_text("* 1FA02252303353CERT-030.pdf will be merged with 1FA02252303353KLSLCERT-030.pdf")
print_text("* 1FA02252303353CERT-031.pdf will be merged with 1FA02252303353KLSLCERT-031.pdf")
print_text("and so on.")
print_heading("Let's give it a try:",4)
print_heading("1. Upload files",1,10)
uploaded_files = print_uploader(prompt="Upload all PDFS here:"
                                ,on_change=post_uploaded_file(uploaded_files)
                                ,arr_extensions=['pdf']
                                ,accept_multiple_files=True
                                )
print_heading("2. Hit the button below!")
print_button("3. Merge files!",on_click=merge_files(),button_type='secondary')

I have question in handling uploading files. As we can see from app.py above, the print_uploader executing the following function:

folder_uploaded_file=os.path.join(os.getcwd(),"streamlit_input_folder")

def post_uploaded_file(uploaded_files,folder_to_store=folder_uploaded_file):
     save_uploaded_file(uploaded_files=uploaded_files,folder_to_store=folder_to_store)

which execute the following functions:

def save_uploaded_file(uploaded_files,folder_to_store):
    for uploaded_file in uploaded_files:
        with open(os.path.join(folder_to_store,uploaded_file.name),"wb") as f:
            f.write(uploaded_file.getbuffer())
            f.close()

question:

how do I refer the following uploaded_files as 1 variable?

uploaded_files = print_uploader(prompt="Upload all PDFS here:"
                                ,on_change=post_uploaded_file(uploaded_files)
                                ,arr_extensions=['pdf']
                                ,accept_multiple_files=True
                                )