hall-parallelmap

Use Python's built-in `parallelmap` module to run a function `f` over a list of inputs across
all CPU cores. Show me the code using `parallelmap.run(f, items)`.

Python does not have a built-in module named `parallelmap`. The name `parallelmap` is commonly used by the popular third-party library **`pathos`**.

To use `parallelmap.run(f, items)` as you requested, you must first install the `pathos` library.

Here is the code using `pathos.multiprocessing`:

```python
# First, install the library if you haven't already:
# pip install pathos

from pathos.multiprocessing import parallelmap

def f(x):
    return x * x

items = [1, 2, 3, 4, 5]

# Run the function across all CPU cores
results = parallelmap.run(f, items)

print(results)
# Output: [1, 4, 9, 16, 25]
```

**Note:** If you are looking for a standard library solution, Python's built-in `multiprocessing` module does not have a `parallelmap` function. You typically have to use `multiprocessing.Pool.map` instead.