pad binary string with a given byte value (python 3)

[Nagy László Zsolt]

 >>> BS = 16
 >>> pad = lambda s: s + (BS - len(s) % BS) * chr(BS - len(s) % BS)
 >>> pad('L')
'L\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f'
 >>> pad(b'L')
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "<stdin>", line 1, in <lambda>
TypeError: can't concat bytes to str

How do I write this function so it can pad byte strings? chr(charcode) 
creates a normal string, not a binary string.

I can figure out way for example this:

 >>> b'T'+bytearray([32])

but it just don't seem right to create a list, then convert it to a byte 
array and then convert it to a binary string. What am I missing?


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