What is the functools.lru_cache decorator?

Question

Accepted Answer

**@lru_cache** caches function results based on arguments.

```python
from functools import lru_cache

@lru_cache(maxsize=128)
def fibonacci(n):
    if n < 2:
        return n
    return fibonacci(n-1) + fibonacci(n-2)

print(fibonacci(100))  # Fast! Cached results

# Cache info
print(fibonacci.cache_info())
# CacheInfo(hits=98, misses=101, maxsize=128, currsize=101)

# Clear cache
fibonacci.cache_clear()

# Without arguments (Python 3.9+)
from functools import cache

@cache
    def expensive(x):
        return x ** 2

# Custom key function
from functools import lru_cache

def custom_key(args, kwargs):
    return (args, tuple(sorted(kwargs.items())))

@lru_cache(maxsize=128, key=custom_key)
def api_call(url, timeout=30):
    return requests.get(url, timeout=timeout)

# Caching with dict (no maxsize)
cache = {}

def cached_function(n):
    if n not in cache:
        cache[n] = expensive_computation(n)
    return cache[n]
```

**LRU = Least Recently Used:**
- Evicts oldest used when full.
- `maxsize=None` for unlimited cache.
- Works with hashable arguments only.

Python: What is the functools.lru_cache decorator?