When running the following code on Windows 7 (64bit os), and selecting a root drive letter, eg C:, it returns "C:/", with a slash appended. When selecting any other path below root level, eg "C:/users" it returns "C:/users" - no slash appended. 
This then introduces an odd edge case in processing the output if the path is to be prepended to directory walk data and other file names.

Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:18:55) [MSC v.1900 64 bit (AMD64)] on win32

>>> from tkinter import filedialog
>>> SourcePath = filedialog.askdirectory()
>>> print(SourcePath)
C:/
>>> SourcePath = filedialog.askdirectory()
>>> print(SourcePath)
C:/NVIDIA
>>>