Problem with Add field and calculate field

Question

I'm writing a python script that needs to create a polygon feature class which has add to it a "A" field from its input. But, when i run the script, this message appear "<type 'exceptions.RuntimeError'>: ERROR 999999: Error executing function. A locator with this name does not exist. Failed to execute (script)." 
I'm using ArcGis 9.3. Anybody knows if there is a problem with the script? what the message means?

alifardy · Answer

how to calculate float number (such as 2,4 ; 3,7 ; -5,1) in a table? because in python, float number use point(.) not comma(,). but in table, float number use comma.

error script :
a = 3,4
pow(10,a) --> error

but if a = 3.4
pow(10,a) --> work

DaleHoneycutt · Answer

i already know the problem, but i have another problem with CalculateField or CalculateValue function in python script. How to calculate sum of value in a column of table?

Use the Summary Statistics tool

alifardy · Answer

i already know the problem, but i have another problem with CalculateField or CalculateValue function in python script. How to calculate sum of value in a column of table?