how to define a static field of a given class

[feel_energetic]

thanks for all of your replies

I did this before I posted the subject but got (NameError: global name
'startTime' is not defined)

the most important thing i didn't know is
"the static field should be referred with the qualifier ClassName"

it's a little different from C++ :)  (the static field can directly
referred without the ClassName)