Limitations of the "file" protocol

The HTML files stored in a computer can be loaded in the browser in two different ways:

by the File / Open browser menu: in this case the browser uses the "file" protocol (the address in the address bar starts with file://)
by launching a local web server (for instance the one provided by Python standard distribution: python -m http.server) and entering the file address in the browser address bar (for instance localhost:8000//app.html). The protocol is "http" (or "https")

These options are mostly the same, but the "file" protocol comes with a few limitations:

external scripts cannot be loaded with the syntax <script type="text/python" src="test.py"></script>
it is not possible to import modules or packages located in the same directory as the application
files cannot be opened and read with open()

The reason is that these features rely on Ajax calls to get the modules / packages source code, or the file contents; and browsers do not allow making Ajax calls when the protocol is "file".

With this protocol, it is always possible to import the modules in the standard library if the file brython_stdlib.js is loaded in the page, as well as Brython packages, or the modules bundled in file brython_modules.js created by the command brython-cli modules (cf. section import implementation).

Introduction

Installation

Limitations of the "file" protocol

Frequently asked questions

Syntax, keywords and built-in functions

Standard distribution

`import` implementation

Brython packages

Browser interface

Brython-specific built-in modules

Working with Brython

Cookbook

Limitations of the "file" protocol