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Brython not playing well with Opal.

See original GitHub issue

I am trying to get Opal (Ruby for JS) to play well with Brython.

But for some reason if Opal is loaded before Brython, and i then try to import datetime, i get an error.

If i remove the script that loads Opal, the error goes away again.

Minimal example that has the error:

<!doctype html>
<html>
  <head>
    <script src="https://cdn.opalrb.com/opal/1.0.0/opal.min.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/brython@3.8.8/brython.min.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/brython@3.8.8/brython_stdlib.js"></script>
  </head>
  <body onload="brython(1)">
    <script type="text/python">
    import datetime
    </script>
  </body>
</html>

The error is:

Javascript exception: TypeError: Cannot read property 'length' of undefined
    at Object.$B.$getattr (brython.js:6908)
    at _is_dst3982 (eval at exec_module (brython.js:9272), <anonymous>:428:91)
    at eval (eval at exec_module (brython.js:9272), <anonymous>:733:65)
    at exec_module (brython.js:9272)
    at t (brython.js:6570)
    at s (brython.js:6574)
    at Object.e.import_hooks (brython.js:13989)
    at $B.$__import__ (brython.js:9428)
    at Object.$B.$import (brython.js:9472)
    at eval (eval at exec_module (brython.js:9272), <anonymous>:16:8)

Issue Analytics

State:
Created 3 years ago
Comments:5 (2 by maintainers)

Top GitHub Comments

2reactions

PierreQuentelcommented, Apr 3, 2020

The latest commit changes an internal attribute $value used by Brython for instances of subclasses of int or float to a more specific $brython_value. Opal apparently sets the attribute $value for numbers, which caused the incompatibility.

2reactions

PierreQuentelcommented, Apr 2, 2020

@dkgof Interesting !

In Brython, the class of an object is usually determined by its attribute __class__ but, for a reason that I don’t remember, the attribute $class was used instead for a particular class (module), so this attribute $class was tested in the function that gets an object’s class.

Unfortunately, it seems that Opal sets an attribute $class to Javascript’s Date objects…

In the commit referenced above I have removed the use of $class in Brython, and your code now works. I leave the issue open for the moment, in case you find other incompatibilities.

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