TypeError: descriptor '__init__' requires a 'super' object but received a 'str'

Your super call giving the error in the Developer class should be:

super(Developer, self).__init__(f, l, a) 

In the Manager class:

super(Manager, self).__init__(f, l, a)

You have other issues, for example, in Employee you have two attributes called raise_amount, one is a float and one is a method (function). That's not allowed and the float takes precedence, so dev1.raise_amount() fails.

In print_employee() you mis-spell emp.fullname

Change all of your super.__init__(...) calls to super().__init__(...). The problem was the missing pair of parentheses ().

From the official Python 3.3 reference here, super is actually a built-in function with the signature super([type[, object-or-type]]).