Python: determining if a number is in a sorted array -

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i know 1 way determine if object in array:

if object in array:     print "object in array" 

however can slow if array large. assume algorithm works looking @ every object in array , compares object being searched for. if know array sorted (low high) algorithm can stop looking once object in array larger object being searched (and conclude object not in array). how efficiently implemented in python?