Bash is not a programming language, but a shell targetted for quickly entering commands and executing those. Therefore, you run other commands doing your job (e.g. mv moves files and directories). Variables in Bash are limited and since commands are all strings, there is no reason to be very strict on it. (it is possible though to force types, see help declare).

Python on the other hand is a more extensive programming language with more language features. Instead of executing other programs, you use built-in functions or other functionality from modules (libraries in other languages). For a basic tutorial on input/output in Python, see http://docs.python.org/tutorial/inputoutput.html. The whole tutorial itself is worth reading if you want to start programming in Python.