Problem scenario
You are taking a slice of a Python string. You know that syntax like var_x[-2:] signifies the penultimate character and the last character of a string (called var_x). But you are only seeing one character -- not two. You expect to see two (or a different number of characters than what you are seeing). Why is the snippet printing out fewer characters than you expect?
Possible Solution #1
There could be an invisible "\n" attached to the string (e.g., at the end of the line). If you are using "readlines" to read an input file, there could be a "new line" or "line break" being processed as a single character. You may be seeing an incorrect number of characters in your slice/portion. If you are reading a file, and processing it line by line, you may want to use the .strip() function. This can remove the "\n" character that is getting picked up and ruining otherwise sound logic for your string manipulation task.
Possible Solution #2
There is an "if" or "for" loop or some logic in your program that is causing a special case to not process the way you are thinking about it. Sometimes a condition is met where a portion of code is entered or skipped, but we humans forget about this scenario. Use some intermediate print statements; this may be tedious, but you may be able to pinpoint the problem.