How to calculate memory usage of a program?

I am implementing a online judge in python. The judge is to run on a UNIX machine. To enforce memory limits I am using ulimit and to run a program I am using subprocess.Popen() . I want to calculate the exact memory usage. How can I do so?

did you try $pmap pid ?

Yes I tried that.

https://raw.github.com/pixelb/ps_mem/master/ps_mem.py

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