As demonstrated, Python didn't require a function def, but again to illuminate:
s = "ABC"
list(map(lambda a: (('0'*8)+bin(ord(a))[2:])[-8:],s))
=> ['01000001', '01000010', '01000011']
Having said that, I generally prefer functions, as they improve read-ability of the code.
Glad you're digging Ruby. I studied it for quite awhile but I'm preferring Python.
PS: You didn't return a list.
:P