How to extract a substring from a string using position and length

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@proc8888

I need to extract a substring from 4th position for a length of 2 characters.

pos4th = 4 - 1     # 3
len2 = pos4th + 2  # 5

abc = 'abcdefghijk'
de = abc[pos4th:len2]

print abc, de, ENTER, pos4th, len2
exit()