Question about math.pi is mutable

[wangq at travelsky.com]

Hello, python-list guys:

    I am a newbie of python from Beijing. China. 
    I have a question about "math.pi". 
    As you can see in the attachment, why i can modify "math.pi"?
    (in "mathmodule.c" "pi" is a "static const double")
    
Thank you in advance!

Best Wishes！