python - Why does my function return None? -

this may easy question answer, can't simple program work , it's driving me crazy. have piece of code:

def dat_function():     my_var = raw_input("type \"a\" or \"b\": ")      if my_var != "a" , my_var != "b":         print  "you didn't type \"a\" or \"b\".  try again."         print " "         dat_function()     else:         print my_var, "-from dat_function"         return my_var   def main():     print dat_function(), "-from main()"  main() 

now, if input "a" or "b",everything fine. output is:

type "a" or "b": a -from dat_function -from main() 

but, if type else , "a" or "b", this:

type "a" or "b": purple didn't type "a" or "b".  try again.  type "a" or "b": a -from dat_function none -from main() 

i don't know why dat_function() returning none, since should return my_var. print statement shows my_var correct value, function doesn't return value reason.

it returning none because when recursively call it:

if my_var != "a" , my_var != "b":     print  "you didn't type \"a\" or \"b\".  try again."     print " "     dat_function() 

..you don't return value.

so while recursion happen, return value gets discarded, , fall off end of function. falling off end of function means python implicitly returns none, this:

>>> def f(x): ...     pass >>> print(f(20)) none 

so, instead of calling dat function() in if statement, need return it.