download a file if not already downloaded

dl.py

# download file if not already downloaded
def dl(url, file=None):
    from urllib.request import urlretrieve
    from urllib.parse import urlparse
    import os.path
    if file is None:
        file = os.path.basename(urlparse(url).path)
    if not os.path.exists(file):
        urlretrieve(url, file)
    return file

# get SED templates
sed_fits = fits.open(dl('https://github.com/blanton144/kcorrect/raw/master/data/templates/k_nmf_derived.default.fits'))

# can specify name of downloaded file as well
sed_fits = fits.open(dl('https://github.com/blanton144/kcorrect/raw/master/data/templates/k_nmf_derived.default.fits', 'templates.fits'))