L6·Expert

🚀Performance & slots

Profiling, __slots__, and when to reach for C.

performanceprofile__slots__cython

§ 1Measure first

cProfile, timeit, and py-spy. Don't optimize before you profile.

§ 2slots

Declaring __slots__ on a class skips __dict__ per instance — significant memory savings when you have millions of instances.

§ 3Reach for C

NumPy for numeric arrays. Cython, mypyc, or Rust extensions (via PyO3) when pure-Python is a bottleneck.

Example

1class Point:
2    __slots__ = ("x", "y")
3    def __init__(self, x, y):
4        self.x, self.y = x, y
5
6p = Point(3, 4)
7print(p.x, p.y)
8try:
9    p.z = 5  # AttributeError — no __dict__
10except AttributeError as e:
11    print("blocked:", e)

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__slots__ mainly saves:

Memory, References & gc

🚀Performance & __slots__