Last caracter of a string truncated issue when working from the end of the string

[Teknohead23]

Hello, can someone please explain why when I select a range starting from the end of a string it truncates the last character?
I can work from the front end as variable dst will always be the same length but when faced with an unknown string length it would be an issue

dst = (r"C:\Users\tekno\Documents\Client Drawings\AAA001")
dwg_name = (dst[-7:-1])
print(dst)
print(dwg_name)
print(dst[40:47])
print(dst[-7:-1])
print(dst[-1])

Output:
C:\Users\tekno\Documents\Client Drawings\AAA001
\AAA00
\AAA001
\AAA00
1