How to make this dictionary-generating code more efficient?

[jefsummers]

Delete line 9 (if you do the rest below)
Delete lines 13-16
Change 17 to

cipher_dict = {a:b for (a,b) in zip(sndlst,str)}

though I agree with not using str as a variable.
Delete 18-20, move the print statement to after line 23 (style issue - your function is called make_cipher_dict, not print it, so would change 21 to return the dictionary and print it from the main program. That makes the function much more re-usable)