util.py

import requests
from pathlib import Path
import time 

def fetch_and_cache(data_url, file, data_dir="data", force=False):
    """
    Download and cache a url and return the file object.
    
    data_url: the web address to download
    file: the file in which to save the results.
    data_dir: (default="data") the location to save the data
    force: if true the file is always re-downloaded 
    
    return: The pathlib.Path object representing the file.
    """
    
    ### BEGIN SOLUTION
    data_dir = Path(data_dir)
    data_dir.mkdir(exist_ok = True)
    file_path = data_dir / Path(file)
    # If the file already exists and we want to force a download then
    # delete the file first so that the creation date is correct.
    if force and file_path.exists():
        file_path.unlink()
    if force or not file_path.exists():
        print('Downloading...', end=' ')
        resp = requests.get(data_url)
        with file_path.open('wb') as f:
            f.write(resp.content)
        print('Done!')
        last_modified_time = time.ctime(file_path.stat().st_mtime)
    else:
        last_modified_time = time.ctime(file_path.stat().st_mtime)
        print("Using cached version that was downloaded (UTC):", last_modified_time)
    return file_path
    ### END SOLUTION