>>> from perfums import selecciona

>>> selecciona ('perfums.txt', 'EAU_PARFUM', 'eauparfum.txt')
>>> with open ('eauparfum.txt', 'r') as f:
...    s = f.read()
>>> s
'Challenge 0.78\nEau-de-Lachette 1.31\nMumu 0.78\n'
>>> selecciona ('perfums.txt', 'EAU_COLOGNE', 'eaucologne.txt')
>>> with open('eaucologne.txt', 'r') as f:
...    s = f.read()
>>> s
'Gege 0.21\nLala 0.3\nLolo 0.3\n'