Is Python Interpreted, or Compiled, or Both

Is Python interpreted, or compiled, or both?

First off, interpreted/compiled is not a property of the language but a property of the implementation. For most languages, most if not all implementations fall in one category, so one might save a few words saying the language is interpreted/compiled too, but it's still an important distinction, both because it aids understanding and because there are quite a few languages with usable implementations of both kinds (mostly in the realm of functional languages, see Haskell and ML). In addition, there are C interpreters and projects that attempt to compile a subset of Python to C or C++ code (and subsequently to machine code).

Second, compilation is not restricted to ahead-of-time compilation to native machine code. A compiler is, more generally, a program that converts a program in one programming language into a program in another programming language (arguably, you can even have a compiler with the same input and output language if significant transformations are applied). And JIT compilers compile to native machine code at runtime, which can give speed very close to or even better than ahead of time compilation (depending on the benchmark and the quality of the implementations compared).

But to stop nitpicking and answer the question you meant to ask: Practically (read: using a somewhat popular and mature implementation), Python is compiled. Not compiled to machine code ahead of time (i.e. "compiled" by the restricted and wrong, but alas common definition), "only" compiled to bytecode, but it's still compilation with at least some of the benefits. For example, the statement a = b.c() is compiled to a byte stream which, when "disassembled", looks somewhat like load 0 (b); load_str 'c'; get_attr; call_function 0; store 1 (a). This is a simplification, it's actually less readable and a bit more low-level - you can experiment with the standard library dis module and see what the real deal looks like. Interpreting this is faster than interpreting from a higher-level representation.

That bytecode is either interpreted (note that there's a difference, both in theory and in practical performance, between interpreting directly and first compiling to some intermediate representation and interpret that), as with the reference implementation (CPython), or both interpreted and compiled to optimized machine code at runtime, as with PyPy.

What's preventing python from being compiled?

Python, the language, like any programming language, is not in itself compiled or interpreted. The standard Python implementation, called CPython, compiles Python source to bytecode automatically and executes that via a virtual machine, which is not what is usually meant by "interpreted".

There are implementations of Python which compile to native code. For example, the PyPy project uses JIT compilation to get the benefits of CPython's ease of use combined with native code performance.

Cython is another hybrid approach, generating and compiling C code on the fly from a dialect of Python.

However, because Python is dynamically typed, it's not generally practical to completely precompile all possible code paths, and it won't ever be as fast as mainstream statically typed languages, even if JIT-compiled.

Is Python interpreted (like Javascript or PHP)?

There's multiple questions here:

1. No, Python is not interpreted. The standard implementation compiles to bytecode, and then executes in a virtual machine. Many modern JavaScript engines also do this.
2. Regardless of implementation (interpreter, VM, machine code), anything you want can run in the background. You can run shell scripts in the background, if you want.

If Python is interpreted, what are .pyc files?

They contain byte code, which is what the Python interpreter compiles the source to. This code is then executed by Python's virtual machine.

Python's documentation explains the definition like this:

Python is an interpreted language, as
opposed to a compiled one, though the
distinction can be blurry because of
the presence of the bytecode compiler.
This means that source files can be
run directly without explicitly
creating an executable which is then
run.

Is python program/executable portable?

Most probably you will have read somewhere that the Python language is an interpreted programming or a script language. The truth is: Python is both an interpreted and a compiled language. But calling Python a compiled language would be misleading.
People would assume that the compiler translates the Python code into machine language but this is not the way python code is executed. Python code is translated into intermediate code, which has to be executed by a virtual machine, known as the PVM, the Python virtual machine. This is a similar approach to the one taken by Java. There is even a way of translating Python programs into Java byte code for the Java Virtual Machine (JVM). This can be achieved with Jython. The default implementation of python is Cython but there is more like Jython, PyPy,IronPython and more!

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