Question from a beginner

[Rodney Dunning]

Hello,

I've just picked up python to create some 3D visuals (using VPython)
for a physics class I'm developing. While writing a program, I
developed a "bug" that is reflected in the code below. When executed,
*both* Test1 and Test2 are changed. Can someone explain this to me?
Why is Test2 changed?

from visual import *
from __future__ import division

##Variable tester

a = vector(1,0,0)

Test1 = a

Test2 = a

print "Test1 = ",Test1
print "Test2 = ",Test2

Test1.x += 3

print "Test1 = ",Test1
print "Test2 = ",Test2

##End code

I've programmed extensively in Fortran-90. Is there anything in python
analogous to the PARAMETER keyword in Fortran-90, such as

integer, PARAMETER :: i = 10  !*** the value of i cannot be changed,
period.

Thanks for your help.

--
Rodney Dunning
Assistant Professor of Physics
Birmingham-Southern College