event_handler.py

#Event handler for upload button
def upload_btn_eventhandler(obj):
    
    #Clear output before each run
    with data_process_output:
        clear_output()
    
    #Read file
    for file_name in upload_file.value:
        
        #Split file name to extract data
        extension = file_name.split('.')[1]
        content = upload_file.value[file_name]['content']

        if(extension == 'xlsx' or extension == 'xls'):
            data = pd.read_excel(BytesIO(content))
            
        elif(extension == 'csv'):
            data = pd.read_csv(BytesIO(content))
        
        else:
            print("File not accepted")
            
    # Calling another function to filter data (next step)
    # filter_data(data)

    return data