python-performance-optimization（Python 性能 optimization）

Python Performance Optimization

Profile, analyze, and optimize Python code for better performance - CPU profiling, memory optimization, and implementation best practices.

When to Invoke

• User reports slow Python code or asks to speed up execution
• Profiling or benchmarking Python applications
• Reducing CPU time, memory consumption, or I/O wait
• Optimizing database queries or data processing pipelines
• Debugging memory leaks or excessive memory usage
• Choosing between parallelization strategies (threading, multiprocessing, async)
• Evaluating algorithmic vs implementation-level improvements

Core Concepts

Profiling Types

• CPU Profiling: Identify time-consuming functions (cProfile, py-spy)
• Memory Profiling: Track memory allocation and leaks (tracemalloc, memory_profiler)
• Line Profiling: Profile at line-by-line granularity (line_profiler)
• Call Graph: Visualize function call relationships

Performance Metrics

• Execution Time: How long operations take
• Memory Usage: Peak and average memory consumption
• CPU Utilization: Processor usage patterns
• I/O Wait: Time spent on I/O operations

Optimization Strategies

• Algorithmic: Better algorithms and data structures
• Implementation: More efficient code patterns
• Parallelization: Multi-threading/processing
• Caching: Avoid redundant computation
• Native Extensions: C/Rust for critical paths

Quick Start

import time
import timeit

# Simple timing
start = time.time()
result = sum(range(1000000))
print(f"Execution time: {time.time() - start:.4f} seconds")

# Accurate benchmarking with timeit
execution_time = timeit.timeit("sum(range(1000000))", number=100)
print(f"Average time: {execution_time/100:.6f} seconds")

Profiling Tools Summary

cProfile - CPU Profiling

python -m cProfile -o output.prof script.py
python -m pstats output.prof

line_profiler - Line-by-Line

uv add --dev line-profiler    # or: uv tool install line-profiler
kernprof -l -v script.py

memory_profiler - Memory Usage

uv add --dev memory-profiler
python -m memory_profiler script.py

py-spy - Production Profiling

uv tool install py-spy
py-spy record -o profile.svg -- python script.py
py-spy top --pid 12345

Key Optimization Patterns

Data Structure Selection

• Dict/Set for lookups: O(1) vs O(n) for list search
• Generators for large datasets: Constant memory vs full list
• **slots on classes**: Reduces per-instance memory

Code-Level Optimizations

• List comprehensions over loops (faster C implementation)
• str.join() over += concatenation
• Local variables over global access in hot loops
• Inline simple operations in tight loops
• Built-in functions (implemented in C)

Caching

• functools.lru_cache for expensive pure functions
• weakref.WeakValueDictionary for GC-friendly caches

Parallelization

• multiprocessing: CPU-bound tasks, true parallelism
• threading: I/O-bound tasks with shared memory
• asyncio: I/O-bound tasks with many concurrent operations

Memory Optimization

• tracemalloc for detecting memory leaks (snapshot comparison)
• Iterators over lists for file/stream processing
• weakref caches to allow garbage collection

Database Optimization

• Batch operations with executemany() and single commit
• Index frequently queried columns
• Select only needed columns (avoid SELECT *)
• Use EXPLAIN QUERY PLAN for analysis

Benchmarking

from functools import wraps
import time

def benchmark(func):
    """Decorator to benchmark function execution."""
    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        result = func(*args, **kwargs)
        elapsed = time.perf_counter() - start
        print(f"{func.__name__} took {elapsed:.6f} seconds")
        return result
    return wrapper

For pytest-based benchmarking: pip install pytest-benchmark

Best Practices

1. Profile before optimizing - measure to find real bottlenecks
2. Focus on hot paths - optimize code that runs most frequently
3. Use appropriate data structures - dict for lookups, set for membership
4. Avoid premature optimization - clarity first, then optimize
5. Use built-in functions - they are implemented in C
6. Cache expensive computations - use lru_cache
7. Batch I/O operations - reduce system calls
8. Use generators for large datasets
9. Consider NumPy for numerical operations
10. Profile production code - use py-spy for live systems

Common Pitfalls

• Optimizing without profiling
• Using global variables unnecessarily
• Not using appropriate data structures
• Creating unnecessary copies of data
• Not using connection pooling for databases
• Ignoring algorithmic complexity
• Over-optimizing rare code paths
• Not considering memory usage

Performance Checklist

• Profiled code to identify bottlenecks
• Used appropriate data structures
• Implemented caching where beneficial
• Optimized database queries
• Used generators for large datasets
• Considered multiprocessing for CPU-bound tasks
• Used async I/O for I/O-bound tasks
• Minimized function call overhead in hot loops
• Checked for memory leaks
• Benchmarked before and after optimization

References

• references/optimization-patterns.md - detailed code examples for all profiling tools, optimization patterns (list comprehensions, generators, string concat, dict lookups, local vars, function call overhead), advanced optimization (NumPy, lru_cache, slots, multiprocessing, async I/O), database optimization, memory leak detection, and benchmarking tools

Resources

• cProfile: Built-in CPU profiler
• memory_profiler: Memory usage profiling
• line_profiler: Line-by-line profiling
• py-spy: Sampling profiler for production
• NumPy: High-performance numerical computing
• Cython: Compile Python to C
• PyPy: Alternative Python interpreter with JIT