Question: I am trying to call my python function created. But not getting any output and no resource how to achieve. Code : <!DOCTYPE html> <html> <head> <link rel="stylesheet" href="https://pyscript.net/alpha/pyscript.css" /> <script defer src="https://pyscript.net/alpha/pyscript.js"></script> </head> <body> <p>Click on the "Choose File" button to upload a file:</p> <form> <input type="file" id="myFile" name="filename"> <input type="submit" onClick="readfile(filename)" name="SUBMIT"> </form> <py-script> def readfile(filename): with open(filename) as mfile: head = [next(mfile) for x in range(1,5)] print(head) </py-script> </body> </html>  It would be great helpful if some one provide input like … How to pass selected file to my function and python will be executed & return output on screen.

Answer: When writing Python in the browser, you must rethink how actions are performed. Typically, Python programs are procedural. Browser-based applications are asynchronous. The first step is to enable asynchronous features: import asyncio  Browser based programs cannot directly access the local file system. Your code is not doing what you think it is. def readfile(filename): with open(filename) as mfile: head = [next(mfile) for x in range(1,5)] print(head)  Your code is reading from the browser virtual file system which is allowed. You are trying to process the event from the ` element but trying to access a different location. Note: I do not know what the file contents of "filename" are, so I did not incorporate your code after the file is read. Your code cannot read files. You must ask the browser to read a file for your application. This is performed with the FileReader class. Example: async def process_file(event): # Currently, PyScript print() does not work in this # type of code (async callbacks) # use console.log() to debug output fileList = event.target.files.to_py() for f in fileList: data = await f.text() document.getElementById("content").innerHTML = data # Add your own code to process the "data" variable # which contains the content of the selected file  Another problem is that you are passing a Python function as a callback. That will not work. Instead, you must call create_proxy() to create a callback proxy for the Python function. The browser will call the proxy which then calls your Python function. Example: # Create a Python proxy for the callback function # process_file() is your function to process events from FileReader file_event = create_proxy(process_file) # Set the listener to the callback document.getElementById("myfile").addEventListener("change", file_event, False)  I put a copy of this solution on my website. You can right-click on the page to download the source code. File Example Demo Complete solution: <!DOCTYPE html> <html> <head> <link rel="stylesheet" href="https://pyscript.net/alpha/pyscript.css" /> <script defer src="https://pyscript.net/alpha/pyscript.js"></script> <title>File Example</title> </head> <body> <p>This example shows how to read a file from the local file system and display its contents</p> <br /> <p>Warning: Not every file type will display. PyScript removes content with tags such as XML, HTML, PHP, etc. Normal text files will work.</p> <br /> <p>No content type checking is performed to detect images, executables, etc.</p> <br /> <label for="myfile">Select a file:</label> <input type="file" id="myfile" name="myfile"> <br /> <br /> <div id="print_output"></div> <br /> <p>File Content:</p> <div style="border:2px inset #AAA;cursor:text;height:120px;overflow:auto;width:600px; resize:both"> <div id="content"> </div> </div> <py-script output="print_output"> import asyncio from js import document, FileReader from pyodide import create_proxy async def process_file(event): fileList = event.target.files.to_py() for f in fileList: data = await f.text() document.getElementById("content").innerHTML = data def main(): # Create a Python proxy for the callback function # process_file() is your function to process events from FileReader file_event = create_proxy(process_file) # Set the listener to the callback e = document.getElementById("myfile") e.addEventListener("change", file_event, False) main() </py-script> </body> </html>