How VPython 6 differs from VPython 5

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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.

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<div dir=3D"ltr">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&#39;t &#=
39;__main__&#39; is an unavoidable &quot;feature&quot;, not a bug. That is,=
 there doesn&#39;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.<br>
<div><br></div><div><p class=3D"" style=3D"text-align:justify;margin:6pt 0p=
t 0pt;font-size:10pt;color:rgb(0,0,0);vertical-align:baseline;font-family:s=
ans-serif"><span class=3D"" style=3D"color:rgb(0,0,160);font-weight:bold">C=
hanges from VPython 5</span></p>
<p class=3D"" style=3D"text-align:justify;margin:6pt 0pt 0pt;font-size:10pt=
;color:rgb(0,0,0);vertical-align:baseline;font-family:sans-serif">The new v=
ersion makes an essential change to the syntax of VPython programs. Now, an=
 animation loop=C2=A0<strong><em>MUST</em></strong>=C2=A0contain a=C2=A0<sp=
an class=3D"" style=3D"color:rgb(255,0,0)">rate</span>=C2=A0or=C2=A0<span c=
lass=3D"" style=3D"color:rgb(255,0,0)">sleep</span>=C2=A0statement, which l=
imits the number of loop iterations per second as before but also when appr=
opriate (about 30 times per second) updates the 3D scene and handles mouse =
and keyboard events. Without a=C2=A0<span class=3D"" style=3D"color:rgb(255=
,0,0)">rate</span>=C2=A0or=C2=A0<span class=3D"" style=3D"color:rgb(255,0,0=
)">sleep</span>=C2=A0statement, the scene will not be updated until and unl=
ess the loop is completed.</p>
<p class=3D"" style=3D"text-align:justify;margin:6pt 0pt 0pt;font-size:10pt=
;color:rgb(0,0,0);vertical-align:baseline;font-family:sans-serif">You shoul=
d use the new function=C2=A0<span class=3D"" style=3D"color:rgb(255,0,0)">s=
leep</span>=C2=A0rather than time.sleep. The new function periodically rend=
ers the scene and processes mouse events, making it possible to continue us=
ing zoom and rotate, whereas time.sleep does not do this.</p>
<p class=3D"" style=3D"text-align:justify;margin:6pt 0pt 0pt;font-size:10pt=
;color:rgb(0,0,0);vertical-align:baseline;font-family:sans-serif">You must =
import visual or vis before importing graph or controls or filedialog, whic=
h most users have always done anyway.</p>
<p class=3D"" style=3D"text-align:justify;margin:6pt 0pt 0pt;font-size:10pt=
;color:rgb(0,0,0);vertical-align:baseline;font-family:sans-serif">For techn=
ical 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 t=
he visual module. For this reason, you should import visual near the start =
of your program, because any executable statements preceding the import wil=
l be executed twice. The import of visual is also re-executed, but this is =
harmless because in Python a repeated import doesn&#39;t repeat the calcula=
tions in the imported module.</p>
<p class=3D"" style=3D"text-align:justify;margin:6pt 0pt 0pt;font-size:10pt=
;color:rgb(0,0,0);vertical-align:baseline;font-family:sans-serif"><strong>I=
mporting your own modules:</strong>=C2=A0If 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 dem=
o is the base program (when lib imports visual, that will be the second imp=
ort 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__=3D=3D&#39;=
__main__&#39; won&#39;t work, because the program will be imported by visua=
l. To test a module, import it from a test program rather than trying to us=
e __name__=3D=3D&#39;__main__&#39; within the module.</p>
</div></div>

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