import re
 
sentence = "Machine learning and data mining often employ the same methods and overlap significantly."
 
dic = {'MLDM': ['machine learning and data mining'], 'ML': ['machine learning'],
 'DM': ['data mining']}
 
def get_key(val):
	for k,v in dic.items():
		if m.group().lower() in map(str.lower, v):
			return k
	return ''
 
# Flatten the lists in values and sort the list by length in descending order
l=sorted([v for x in dic.values() for v in x], key=len, reverse=True)
# Build the alternation based regex with \b to match each item as a whole word 
rx=r'\b(?:{})\b'.format("|".join(l))
for m in re.finditer(rx, sentence, re.I): # Search case insensitively
    key = get_key(m.group())
    if key:
	    print("{} {}".format(key, m.start()))
 

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