OS X crashes "No memory", but much of it free

I was running a Python code which may have increased the need for memory. Anyhow, the following happened, and I feel it should not.

• I have 16 GB memory and it shows only 3 GB allocated to Python


• Remainder of memory apparently not allocated to anything


• Should a single application be able to suck that much memory s.t. the rest of OSX becomes vulnerable / non stable?