[Tutor] Help understanding base64 decoding

[Ryan Smith]

Hello All,

I am currently working on a small utility that finds any base64
encoded strings in files and decodes them. I am having issue
understanding how the Base64 module actually works. The regular
expression that I am using correctly matches on the encoded strings. I
simply want to be able to convert the match of the encoded ascii
string to it's decoded ascii equivalent. For example the base64
encoded ascii string 'UwB5AHMAdABlAG0ALgBkAGwAbAA=' will decode to
'System.dll' if I use an online base64 decoder. However I get a
completely different output when trying to codify this using python
3.6.5:

>>>import base64
>>>import binascii

>>>test_str = 'UwB5AHMAdABlAG0ALgBkAGwAbAA='
>>> base64.b64decode(test_str)
b'S\x00y\x00s\x00t\x00e\x00m\x00.\x00d\x00l\x00l\x00'

>>>temp = base64.b64decode(test_str)
>>>binascii.b2a_base64(temp)
b'UwB5AHMAdABlAG0ALgBkAGwAbAA=\n'

I understand that when decoding and encoding you have to use bytes
objects but what I don't understand is why I can't get the proper
conversion of the original ascii string. Can someone please point me
in the right direction?

Thank you,

Ryan