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Furthermore, the operations update etc. are mutations of s,
so wouldn't the definitions

s.update(t)  	s |= t  	return set s with elements added from t
s.intersection_update(t) 	s &= t 	return set s keeping only
elements also found in t
s.difference_update(t) 	s -= t 	return set s after removing
elements found in t
s.symmetric_difference_update(t) 	s ^= t 	return set s with
elements from s or t but not both

be better as 

s.update(t)  	s |= t  	add elements from t to s

etc.?
I'm not sure what the word "return" is doing here.