Lab 06: hypothesis testing

!pip install pooch

# The above command installs the needed `pooch` 3rd-party package if it's not already installed.


import hashlib  # for verifying that the Central Park file is not corrupted
import pathlib  # for constructing paths to the dataset's location on disk
import sys  # for checking if this is a Google Colab session or not
import pooch  # for downloading the dataset from the web, if needed


# Replace "../data" as needed to point to the correct directory for you.
# This can be an *absolute path* or a *relative path*.  One dot, `.`, means
# "this directory", while two dots, `..`, means "go up one directory."
LOCAL_DATA_DIR = "../data"  # If you're in Colab: just ignore this.

# The URL where the dataset can be downloaded from.
DATA_URL = (
    "https://spencerahill.github.io/25f-stat-methods-course/_downloads/"
    "91803b82950d49961a65355c075439b3/central-park-station-data_1869-01-01_2023-09-30.nc"
)

# This HASH_HEX stores a "hash" which we use to verify that the data you end up
# with has not been altered or corrupted compared to the one at the above URL.
HASH_HEX = "85237a4bae1202030a36f330764fd5bd0c2c4fa484b3ae34a05db49fe7721eee"


def create_data_path(
    colab_dir="/content/data", 
    local_dir=LOCAL_DATA_DIR,
    filename="central-park-station-data_1869-01-01_2023-09-30.nc",
):
    """Set the path for the data, whether on colab or a local Jupyter session."""
    is_this_a_colab = "google.colab" in sys.modules
    if is_this_a_colab:
        data_dir = colab_dir 
    else: 
        data_dir = local_dir

    DATA_DIR = pathlib.Path(data_dir)
    DATA_DIR.mkdir(parents=True, exist_ok=True)
    return DATA_DIR / filename


def sha256sum(path: pathlib.Path) -> str:
    """Get the hash of the file at the specified path."""
    return hashlib.sha256(path.read_bytes()).hexdigest()


DATA_PATH = create_data_path()
# Determine if we'll need to download the data, which we'll do if either (a) 
# the data can't be found, or (b) it appears corrupted/modified from the
# "master" file at the above URL.
need_fetch = (not DATA_PATH.exists()) or (sha256sum(DATA_PATH) != HASH_HEX)

# Download the data if needed.
if need_fetch:
    fetched_data = pooch.retrieve(
        url=DATA_URL, 
        known_hash=f"sha256:{HASH_HEX}",
        path=DATA_PATH.parents[0], 
        fname=DATA_PATH.name,
    )
    print(f"\nDownloaded and verified: {fetched_data}")
else:
    print(f"\nVerified existing file at {DATA_PATH}")