I don’t exactly understand how python use memory, and what Python gives with the tracemalloc builtins. Let’s take this exemple:
import tracemalloc import gc L=[1,2,3] tracemalloc.start() gc.collect() L +=  a = L[:] b = [_ for _ in L] del(L) snapshot = tracemalloc.take_snapshot() # 1° way to get memory consumption top_stats = snapshot.statistics('traceback') for stat in top_stats: print(stat) #print(tracemalloc.get_traced_memory()) # 2° way to get memory consumption tracemalloc.stop()
With the 1° method I get:
D:\file.py:13: size=504 B, count=3, average=168 B → for ‘b’
D:\file.py:20: size=416 B, count=1, average=416 B → for ‘snapshot’ (useless)
D:\file.py:12: size=88 B, count=2, average=44 B → for ‘a’
and with the 2° one: (592, 784) # (Courant,Peak)
So we have Courant which is the sum of memory for ‘a’ and ‘b’. But Peak > Courant so why don’t we have the additional memory consumptions given with take_snapshot() builtin ? When one uses some functions, take_snapshot() tells how much memory had been use inside. Why not here?
Secondly, about the values in themselves. Why take_snapshot() gives 2 different sizes for ‘a’ and for ‘b’ (88 and 504) ? And we get sys.getsizeof(a)=88 and sys.getsizeof(b)=88. So what does size=504 for ‘b’ mean?
Finally, why L +=  doesn’t take any memory space? More simply, if one does c=12 or c=12.0 or c=‘azerty’ or c=(1,2) … (every instanciation of not mutable objects, I would say), it’s invisible for both functions of ‘tracemalloc’. However it isn’t for sys.getsizeof(.)!
So I don’t understand how I can found the memory consumption (Courant, Peak and line-by-line).
My aim is to compare different script to see which one is the less expensive in memory. So, I’m asking for the memory specifically used by a variable (to compare the memory consumption for the variables at the end of my script), but also for the memory used during the script execution (so the peak or the line-by-line consumption)
Thanks for your answers!