If this is what you mean:
import re
txt="I like to eat apple. Me too. Let's go buy some apples."
define_words = 'some apple'
print re.findall(r"([^.]*?%s[^.]*\.)" % define_words,txt)
Output: [" Let's go buy some apples."]
You can also try with:
define_words = raw_input("Enter string: ")
Check if the sentence contain the defined words:
import re
txt="I like to eat apple. Me too. Let's go buy some apples."
words = 'go apples'.split(' ')
sentences = re.findall(r"([^.]*\.)" ,txt)
for sentence in sentences:
if all(word in sentence for word in words):
print sentence