block1.py

from datetime import datetime, timedelta
import subprocess
import shutil

def download_files(datetime_0, datetime_nb):
    '''
    Download files from FTP server.

    Arguments:
        - datetime_0: date from which to download.
        - datetime_nb: number of dates (~files) to download.

    Returns:
        - filenames: list of file names to be downloaded.
        - datetimes: list of dates corresponding to the downloaded files.
    '''
    datetimes = [datetime_0 + timedelta(hours=3*i) for i in range(datetime_nb)]
    urls, filenames = [], []
    for dt in datetimes:
        year = dt.year
        month = str(dt.month).zfill(2)
        day = str(dt.day).zfill(2)
        hour = str(dt.hour).zfill(2)
        # file name changed suddenly one day
        if dt < datetime(2012, 11, 7, 6):
            filename = f'3B42RT.{year}{month}{day}{hour}.7R2.bin.gz'
        else:
            filename = f'3B42RT.{year}{month}{day}{hour}.7.bin.gz'
        urls.append(f'ftp://trmmopen.gsfc.nasa.gov/pub/merged/3B42RT/{year}/'
                    f'{month}/{filename}')
        filenames.append(filename)
    with open('trmm_file_list.txt', 'w') as f:
        f.write('\n'.join(urls))
    shutil.rmtree('trmm_data', ignore_errors=True)
    subprocess.check_call(f'aria2c -x 4 -i trmm_file_list.txt -d trmm_data '
                          '--continue=true'.split(),
                          stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
    return filenames, datetimes