[Visualpython-users] How VPython 6 differs from VPython 5

[Bruce S. <Bru...@nc...>]

Here is detailed information on how VPython 6 differs from VPython 5, which
will be incorporated in the Help for upcoming releases of VPython 6. Note
that the fact that in a main program __name__ isn't '__main__' is an
unavoidable "feature", not a bug. That is, there doesn't seem to be a way
to make this work. As described below, the way to test a module is to
import it from a test routine.

Changes from VPython 5

The new version makes an essential change to the syntax of VPython
programs. Now, an animation loop *MUST* contain a rate or sleep statement,
which limits the number of loop iterations per second as before but also
when appropriate (about 30 times per second) updates the 3D scene and
handles mouse and keyboard events. Without a rate or sleep statement, the
scene will not be updated until and unless the loop is completed.

You should use the new function sleep rather than time.sleep. The new
function periodically renders the scene and processes mouse events, making
it possible to continue using zoom and rotate, whereas time.sleep does not
do this.

You must import visual or vis before importing graph or controls or
filedialog, which most users have always done anyway.

For technical reasons, it is necessary for VPython 6 to do something rather
unusual. When you import visual (or vis), your own program is in turn
imported by the visual module. For this reason, you should import visual
near the start of your program, because any executable statements preceding
the import will be executed twice. The import of visual is also
re-executed, but this is harmless because in Python a repeated import
doesn't repeat the calculations in the imported module.

*Importing your own modules:* If you create your own module (lib.py, say)
that imports visual, and you import lib from a program named demo.py, you
need to import visual in demo.py before importing lib, so that demo is the
base program (when lib imports visual, that will be the second import of
visual and will not lead to lib being imported by visual). Note that the
standard trick of testing a module on the basis of __name__=='__main__'
won't work, because the program will be imported by visual. To test a
module, import it from a test program rather than trying to use
__name__=='__main__' within the module.