Python Performance

Python performance

Python overhead is per-operation, so wins come from doing fewer Python-level operations: better algorithms first, then batch work into C-backed calls, then compile the hot loop.

Method

1. Profile before touching code. python -m cProfile -s cumtime app.py for call-level, py-spy top --pid N for live processes without restarting, line_profiler for a single hot function. Optimizing an unprofiled guess wastes days; the hot spot is rarely where you think.
2. Fix the algorithm before the language. An O(n^2) membership scan beaten into a set lookup outruns any rewrite. Check data-structure fit: list for order, set/dict for membership, deque for both-ends, heapq for top-k.
3. Vectorize numeric loops. A numpy expression over an array replaces a Python loop with one C loop, commonly 10-100x. The trap is accidental element-wise Python (calling float() per item, object-dtype arrays); keep dtypes numeric and operations whole-array.
4. Cut allocation and attribute churn in hot loops. Hoist self.method and global lookups to locals, reuse buffers, prefer comprehensions over append loops. These 10-30% wins are free but only matter inside the measured hot path.
5. Escalate to compiled code deliberately. Order of preference: an existing C-backed library (numpy, polars, re2), functools.lru_cache over recomputation, Cython or a small Rust extension (pyo3/maturin) for the one hot function. Keep the compiled surface minimal; it is the code you can no longer read in a debugger.
6. Verify with a benchmark, not a feeling. timeit or pytest-benchmark with realistic data sizes, before and after, committed next to the code so regressions are visible.

Boundaries

• Do not optimize I/O-bound code with these techniques; overlap the waiting instead (async, threads, batching requests).
• Free-threaded and JIT builds change constants, not complexity; algorithmic wins carry across interpreters, micro-tricks may not.
• Readability is a cost you pay forever; take the 2x that keeps the code plain over the 2.3x that obfuscates it.