If sep is not specified or is None, a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with a None separator returns [].

yes
input_list=[[16,23],[73,1],[56,20],[1,-1]]

tested you code and it returned False,but it gave me one i instead two (i,I)

i and its count 1
s and its count 2
False

i would converted the input string into either lowercase or upperase and then do the count ( in this test the letter case does't matter)
also, you only check one condition --> if chars.islower(), so the code will miss (upper case I)