Memory usage __dict__ vs __slots__

dict.py

import string
import random

long_key = "a_key_with_a_very_long_name_"


class Test:
    def __init__(self):
        for i in range(20):
            v = "".join(random.choices(string.ascii_lowercase, k=20))
            setattr(self, f"{long_key}{i:02}", v)

mem_test.py

import sys
import resource
import importlib

module = None
if len(sys.argv) == 2:
    module_name = sys.argv[1].replace(".py", "")
    module = importlib.import_module(module_name)
else:
    print(f"Usage: {sys.argv[0]} <class-module-to-test>")

fmt = "Selected Test type: {.__name__}.{.__name__}"
print(fmt.format(module, module.Test))
cls = module.Test

NUM_CLASSES = 10**6
mem_init = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
print(f"Creating {NUM_CLASSES:,} {cls.__qualname__!r} instances")
instances = [cls() for _ in range(NUM_CLASSES)]
mem_final = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
print(f"Initial RAM usage: {mem_init:14,}")
print(f"  Final RAM usage: {mem_final:14,}")

result_mem_test.txt

$ time python mem_test.py dict
Selected Test type: dict.Test
Creating 1,000,000 'Test' instances
Initial RAM usage:     12,058,624
  Final RAM usage:  1,546,305,536

________________________________________________________
Executed in   35.14 secs    fish           external
   usr time   34.74 secs    0.07 millis   34.74 secs
   sys time    0.27 secs    1.13 millis    0.26 secs

$ time python mem_test.py slots
Selected Test type: slots.Test
Creating 1,000,000 'Test' instances
Initial RAM usage:     12,288,000
  Final RAM usage:  1,498,284,032

________________________________________________________
Executed in   35.12 secs    fish           external
   usr time   34.64 secs    0.07 millis   34.64 secs
   sys time    0.25 secs    1.15 millis    0.25 secs

result_vector_test.txt

time python vector_test.py vector
Selected Test type: vector.Vector2d
Creating 10,000,000 'Vector2d' instances
Initial RAM usage:     10,960,896
  Final RAM usage:    901,316,608

________________________________________________________
Executed in    4.77 secs    fish           external
   usr time    4.61 secs    0.09 millis    4.61 secs
   sys time    0.13 secs    1.47 millis    0.13 secs
 
$ time python vector_test.py vector_slots
Selected Test type: vector_slots.Vector2d
Creating 10,000,000 'Vector2d' instances
Initial RAM usage:     10,993,664
  Final RAM usage:    583,335,936

________________________________________________________
Executed in    3.93 secs    fish           external
   usr time    3.81 secs    0.09 millis    3.81 secs
   sys time    0.10 secs    1.73 millis    0.10 secs

slots.py

import string
import random

long_key = "a_key_with_a_very_long_name_"


class Test:
    __slots__ = tuple([f"{long_key}{i:02}" for i in range(20)])

    def __init__(self):
        for i in range(20):
            v = "".join(random.choices(string.ascii_lowercase, k=20))
            setattr(self, f"{long_key}{i:02}", v)

vector.py

class Vector2d:
    def __init__(self, x, y):
        self.x = float(x)
        self.y = float(y)

vector_slots.py

class Vector2d:
    __slots__ = ("x", "y")

    def __init__(self, x, y):
        self.x = float(x)
        self.y = float(y)

vector_test.py

import sys
import resource
import importlib

module = None
if len(sys.argv) == 2:
    module_name = sys.argv[1].replace(".py", "")
    module = importlib.import_module(module_name)
else:
    print(f"Usage: {sys.argv[0]} <class-module-to-test>")

fmt = "Selected Test type: {.__name__}.{.__name__}"
print(fmt.format(module, module.Vector2d))
cls = module.Vector2d

NUM_VECTORS = 10**7
mem_init = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
print(f"Creating {NUM_VECTORS:,} {cls.__qualname__!r} instances")
vectors = [cls(3.0, 4.0) for i in range(NUM_VECTORS)]
mem_final = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
print(f"Initial RAM usage: {mem_init:14,}")
print(f"  Final RAM usage: {mem_final:14,}")