Perl is not really oriented towards interactive development, but toward script execution. Python provide much more support for interactive development, in particular, executing expressions and statements from a command line. The Python interpreter facilitates an interactive style of development. The Swig interface wrapper generator makes it easy to expose a C/C++ program's API as a bunch of Python API's, making it easy to learn an API by scripting the Python wrappers. This also makes a good way to run test suites. Python also has very good integration with TCL's Tk for UI stuff. This library is called Tkinter.
Of course XML is all the rage these days, so Python is incorporating support for XML with the expat XML parser and the addition of a wide character type to handle Unicode.
The last cool thing about Python is that there is an implementation of Python hosted on the Java Virtual Machine. Jython will allow you to write Python code that has access to any Java class. This makes for good prototyping, experimenting, and testing.