wshobson--agents/plugins/python-development/skills/python-performance-optimization/references/advanced-patterns.md

# Python Performance Optimization — Advanced Reference

Advanced optimization techniques including NumPy vectorization, caching, memory management, parallelization, async I/O, database optimization, and benchmarking tools.

## Advanced Optimization

### Pattern 11: NumPy for Numerical Operations

```python
import timeit
import numpy as np

def python_sum(n):
    """Sum using pure Python."""
    return sum(range(n))

def numpy_sum(n):
    """Sum using NumPy."""
    return np.arange(n).sum()

n = 1000000

python_time = timeit.timeit(lambda: python_sum(n), number=100)
numpy_time = timeit.timeit(lambda: numpy_sum(n), number=100)

print(f"Python: {python_time:.4f}s")
print(f"NumPy: {numpy_time:.4f}s")
print(f"Speedup: {python_time/numpy_time:.2f}x")

# Vectorized operations
def python_multiply():
    """Element-wise multiplication in Python."""
    a = list(range(100000))
    b = list(range(100000))
    return [x * y for x, y in zip(a, b)]

def numpy_multiply():
    """Vectorized multiplication in NumPy."""
    a = np.arange(100000)
    b = np.arange(100000)
    return a * b

py_time = timeit.timeit(python_multiply, number=100)
np_time = timeit.timeit(numpy_multiply, number=100)

print(f"\nPython multiply: {py_time:.4f}s")
print(f"NumPy multiply: {np_time:.4f}s")
print(f"Speedup: {py_time/np_time:.2f}x")
```

### Pattern 12: Caching with functools.lru_cache

```python
from functools import lru_cache
import timeit

def fibonacci_slow(n):
    """Recursive fibonacci without caching."""
    if n < 2:
        return n
    return fibonacci_slow(n-1) + fibonacci_slow(n-2)

@lru_cache(maxsize=None)
def fibonacci_fast(n):
    """Recursive fibonacci with caching."""
    if n < 2:
        return n
    return fibonacci_fast(n-1) + fibonacci_fast(n-2)

# Massive speedup for recursive algorithms
n = 30

slow_time = timeit.timeit(lambda: fibonacci_slow(n), number=1)
fast_time = timeit.timeit(lambda: fibonacci_fast(n), number=1000)

print(f"Without cache (1 run): {slow_time:.4f}s")
print(f"With cache (1000 runs): {fast_time:.4f}s")

# Cache info
print(f"Cache info: {fibonacci_fast.cache_info()}")
```

### Pattern 13: Using __slots__ for Memory

```python
import sys

class RegularClass:
    """Regular class with __dict__."""
    def __init__(self, x, y, z):
        self.x = x
        self.y = y
        self.z = z

class SlottedClass:
    """Class with __slots__ for memory efficiency."""
    __slots__ = ['x', 'y', 'z']

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

# Memory comparison
regular = RegularClass(1, 2, 3)
slotted = SlottedClass(1, 2, 3)

print(f"Regular class size: {sys.getsizeof(regular)} bytes")
print(f"Slotted class size: {sys.getsizeof(slotted)} bytes")

# Significant savings with many instances
regular_objects = [RegularClass(i, i+1, i+2) for i in range(10000)]
slotted_objects = [SlottedClass(i, i+1, i+2) for i in range(10000)]

print(f"\nMemory for 10000 regular objects: ~{sys.getsizeof(regular) * 10000} bytes")
print(f"Memory for 10000 slotted objects: ~{sys.getsizeof(slotted) * 10000} bytes")
```

### Pattern 14: Multiprocessing for CPU-Bound Tasks

```python
import multiprocessing as mp
import time

def cpu_intensive_task(n):
    """CPU-intensive calculation."""
    return sum(i**2 for i in range(n))

def sequential_processing():
    """Process tasks sequentially."""
    start = time.time()
    results = [cpu_intensive_task(1000000) for _ in range(4)]
    elapsed = time.time() - start
    return elapsed, results

def parallel_processing():
    """Process tasks in parallel."""
    start = time.time()
    with mp.Pool(processes=4) as pool:
        results = pool.map(cpu_intensive_task, [1000000] * 4)
    elapsed = time.time() - start
    return elapsed, results

if __name__ == "__main__":
    seq_time, seq_results = sequential_processing()
    par_time, par_results = parallel_processing()

    print(f"Sequential: {seq_time:.2f}s")
    print(f"Parallel: {par_time:.2f}s")
    print(f"Speedup: {seq_time/par_time:.2f}x")
```

### Pattern 15: Async I/O for I/O-Bound Tasks

```python
import asyncio
import aiohttp
import time
import requests

urls = [
    "https://httpbin.org/delay/1",
    "https://httpbin.org/delay/1",
    "https://httpbin.org/delay/1",
    "https://httpbin.org/delay/1",
]

def synchronous_requests():
    """Synchronous HTTP requests."""
    start = time.time()
    results = []
    for url in urls:
        response = requests.get(url)
        results.append(response.status_code)
    elapsed = time.time() - start
    return elapsed, results

async def async_fetch(session, url):
    """Async HTTP request."""
    async with session.get(url) as response:
        return response.status

async def asynchronous_requests():
    """Asynchronous HTTP requests."""
    start = time.time()
    async with aiohttp.ClientSession() as session:
        tasks = [async_fetch(session, url) for url in urls]
        results = await asyncio.gather(*tasks)
    elapsed = time.time() - start
    return elapsed, results

# Async is much faster for I/O-bound work
sync_time, sync_results = synchronous_requests()
async_time, async_results = asyncio.run(asynchronous_requests())

print(f"Synchronous: {sync_time:.2f}s")
print(f"Asynchronous: {async_time:.2f}s")
print(f"Speedup: {sync_time/async_time:.2f}x")
```

## Database Optimization

### Pattern 16: Batch Database Operations

```python
import sqlite3
import time

def create_db():
    """Create test database."""
    conn = sqlite3.connect(":memory:")
    conn.execute("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)")
    return conn

def slow_inserts(conn, count):
    """Insert records one at a time."""
    start = time.time()
    cursor = conn.cursor()
    for i in range(count):
        cursor.execute("INSERT INTO users (name) VALUES (?)", (f"User {i}",))
        conn.commit()  # Commit each insert
    elapsed = time.time() - start
    return elapsed

def fast_inserts(conn, count):
    """Batch insert with single commit."""
    start = time.time()
    cursor = conn.cursor()
    data = [(f"User {i}",) for i in range(count)]
    cursor.executemany("INSERT INTO users (name) VALUES (?)", data)
    conn.commit()  # Single commit
    elapsed = time.time() - start
    return elapsed

# Benchmark
conn1 = create_db()
slow_time = slow_inserts(conn1, 1000)

conn2 = create_db()
fast_time = fast_inserts(conn2, 1000)

print(f"Individual inserts: {slow_time:.4f}s")
print(f"Batch insert: {fast_time:.4f}s")
print(f"Speedup: {slow_time/fast_time:.2f}x")
```

### Pattern 17: Query Optimization

```python
# Use indexes for frequently queried columns
"""
-- Slow: No index
SELECT * FROM users WHERE email = 'user@example.com';

-- Fast: With index
CREATE INDEX idx_users_email ON users(email);
SELECT * FROM users WHERE email = 'user@example.com';
"""

# Use query planning
import sqlite3

conn = sqlite3.connect("example.db")
cursor = conn.cursor()

# Analyze query performance
cursor.execute("EXPLAIN QUERY PLAN SELECT * FROM users WHERE email = ?", ("test@example.com",))
print(cursor.fetchall())

# Use SELECT only needed columns
# Slow: SELECT *
# Fast: SELECT id, name
```

## Memory Optimization

### Pattern 18: Detecting Memory Leaks

```python
import tracemalloc
import gc

def memory_leak_example():
    """Example that leaks memory."""
    leaked_objects = []

    for i in range(100000):
        # Objects added but never removed
        leaked_objects.append([i] * 100)

    # In real code, this would be an unintended reference

def track_memory_usage():
    """Track memory allocations."""
    tracemalloc.start()

    # Take snapshot before
    snapshot1 = tracemalloc.take_snapshot()

    # Run code
    memory_leak_example()

    # Take snapshot after
    snapshot2 = tracemalloc.take_snapshot()

    # Compare
    top_stats = snapshot2.compare_to(snapshot1, 'lineno')

    print("Top 10 memory allocations:")
    for stat in top_stats[:10]:
        print(stat)

    tracemalloc.stop()

# Monitor memory
track_memory_usage()

# Force garbage collection
gc.collect()
```

### Pattern 19: Iterators vs Lists

```python
import sys

def process_file_list(filename):
    """Load entire file into memory."""
    with open(filename) as f:
        lines = f.readlines()  # Loads all lines
        return sum(1 for line in lines if line.strip())

def process_file_iterator(filename):
    """Process file line by line."""
    with open(filename) as f:
        return sum(1 for line in f if line.strip())

# Iterator uses constant memory
# List loads entire file into memory
```

### Pattern 20: Weakref for Caches

```python
import weakref

class CachedResource:
    """Resource that can be garbage collected."""
    def __init__(self, data):
        self.data = data

# Regular cache prevents garbage collection
regular_cache = {}

def get_resource_regular(key):
    """Get resource from regular cache."""
    if key not in regular_cache:
        regular_cache[key] = CachedResource(f"Data for {key}")
    return regular_cache[key]

# Weak reference cache allows garbage collection
weak_cache = weakref.WeakValueDictionary()

def get_resource_weak(key):
    """Get resource from weak cache."""
    resource = weak_cache.get(key)
    if resource is None:
        resource = CachedResource(f"Data for {key}")
        weak_cache[key] = resource
    return resource

# When no strong references exist, objects can be GC'd
```

## Benchmarking Tools

### Custom Benchmark Decorator

```python
import time
from functools import wraps

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

@benchmark
def slow_function():
    """Function to benchmark."""
    time.sleep(0.5)
    return sum(range(1000000))

result = slow_function()
```

### Performance Testing with pytest-benchmark

```python
# Install: pip install pytest-benchmark

def test_list_comprehension(benchmark):
    """Benchmark list comprehension."""
    result = benchmark(lambda: [i**2 for i in range(10000)])
    assert len(result) == 10000

def test_map_function(benchmark):
    """Benchmark map function."""
    result = benchmark(lambda: list(map(lambda x: x**2, range(10000))))
    assert len(result) == 10000

# Run with: pytest test_performance.py --benchmark-compare
```