Brython-specific built-in modules
Working with Brython
Brython implements Python version 3, based on the
Python Language Reference
The implementation takes into account the browsers limitations, in particular
those related to the file system. Writing is impossible, and reading is
limited to the folders accessible with an Ajax request.
Keywords and built-in functions
Brython supports all the keywords and functions of the Python version with the
same version number.
an event to happen, before going to the next instruction. For this reason:
time.sleep() can't be used : functions in module browser.timer such
set_interval() must be used instead
- the built-in function
prompt(). An example in the gallery shows how to simulate
an input function in a custom dialog box.
- for the same reason, and also because the browser has its own implicit
event loop, the CPython
asyncio module is not usable. A Brython-specific
browser.aio, is provided for asynchronous
- the built-in function
open() takes as argument the url of the file to
open. Since it is read with an Ajax call, it must be in the same domain as
the script. The object returned by
open() has the usual reading and access
read, readlines, seek, tell, close.
- by default,
print() will output to the web browser console and so are the
sys.stdout can be assigned to an object
write() method, and this allows for the redirection of output to go
to a window or text area, for example.
- to open a print dialog (to a printer), call
defined in module browser).
Brython doesn't manage reference counting like CPython. Therefore, method
__del__() is not called when a class instance is no more referenced.
Brython is shipped with a part of the CPython standard library.
Some of the modules that are written in C in CPython standard library have
JSON, which implies a few minor differences with the CPython
package; the values
NaN, Infinity, -Infinity which are recognized by
CPython are not in the JSON specification and as such, throw a
with the Brython module.
xml package is not provided because that of the CPython distribution
uses a C module (
The built-in variable
__name__ is set to the value of the attribute
of the script. For instance:
<script type="text/python" id="myscript">
assert __name__ == 'myscript'
If 2 scripts have the same
id, an exception is raised.
For scripts that don't have an explicit
id set :
- if no script has its
id set to
__main__, the first "unnamed" script has
__name__ set to
"__main__". So, if there only one script in the page,
it will be able to run the usual test :
- for the other unnamed scripts,
__name__ is set to a random string starting