Scripting Languages – How Are They Compiled?

It's worth noting that languages are not interpreted or compiled, but rather language implementations either interpret or compile code. You noted that Ruby is an "interpreted language", but you can compile Ruby à la MacRuby, so it's not always an interpreted language.

Pretty much every Python implementation consists of an interpreter (rather than a compiler). The .pyc files you see are byte code for the Python virtual machine (similar to Java's .class files). They are not the same as the machine code generated by a C compiler for a native machine architecture. Some Python implementations, however, do consist of a just-in-time compiler that will compile Python byte code into native machine code.

(I say "pretty much every" because I don't know of any native machine compilers for Python, but I don't want to claim that none exist anywhere.)

There is no technical standard that defines a scripting language. It's just a word that is defined by common usage, and like any other word in common usage, there is no guarantee that all the usages are consistent. Tackling your specific questions:

1. The dynamic code generation they are talking about is machine code. In a classic interpreted language (think BASIC interpreter), each time a line of a script is executed, that line is translated on the spot into native machine code. It's more complicated now, since many scripting languages will be translated into byte code for a virtual machine, and the byte code may get cached.

2. This is where it gets very fuzzy, and changes with time. In ye olden days, pretty much every scripting language was a classic interpreted language. Nowadays many use byte code, virtual machines, and may use Just-in-time compilers. At that point the line between interpreted languages and compiled languages is blurry. Still, I don't know of any language commonly referred to as a scripting language that is compiled in the classic sense of a one time conversion to native machine code.

3. Languages commonly called scripting languages usually provide a suite of high level data structures like sets, lists, and dictionaries, as well as features like regular expressions. There are interpreted languages that don't provide those high level features, and they usually aren't called scripting languages. I don't think many folks would refer to interpreted BASIC or even UCSD Pascal as a scripting language.