What is functools.partial and when to use it?

Question

Accepted Answer

**functools.partial** creates a new function with **some arguments pre-filled**.

```python
from functools import partial

def power(base, exponent):
    return base ** exponent

# Create specialized functions
square = partial(power, exponent=2)
cube = partial(power, exponent=3)

print(square(5))  # 25
print(cube(5))    # 125

# With maps
map(square, [1, 2, 3, 4])  # [1, 4, 9, 16]

# In callbacks
def process(data, callback):
    result = transform(data)
    callback(result)

process(data, partial(save_to_db, table="users"))

# With class methods
from operator import methodcaller
strip = methodcaller("strip")
strip("  hello  ")  # "hello"
```

**Benefits:**
- Cleaner than lambda for partial application.
- Preserves function metadata.
- Faster than lambda.

Python: What is functools.partial and when to use it?