import re
string = 'I love sleeping. I love singing. I love dancing.'
words = ['Swimming', 'Eating', 'Jogging']
pattern = re.compile(r'(?<=I love )\w+(?=\.)')
print pattern.sub(lambda m: words.pop(0), string)
aW1wb3J0IHJlCgpzdHJpbmcgPSAnSSBsb3ZlIHNsZWVwaW5nLiBJIGxvdmUgc2luZ2luZy4gSSBsb3ZlIGRhbmNpbmcuJwp3b3JkcyA9IFsnU3dpbW1pbmcnLCAnRWF0aW5nJywgJ0pvZ2dpbmcnXQoKcGF0dGVybiA9IHJlLmNvbXBpbGUocicoPzw9SSBsb3ZlIClcdysoPz1cLiknKQoKcHJpbnQgcGF0dGVybi5zdWIobGFtYmRhIG06IHdvcmRzLnBvcCgwKSwgc3RyaW5nKQo=