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Terminology: interpreter and compiler

An interpreter reads the source code of the program as written by the programmer, parses the source code, and interprets the instructions on-the-fly. Python is an interpreter and when we are running Python interactively, we can type a line of Python (a sentence) and Python processes it immediately and is ready for us to type another line of Python.
Even though we are typing these commands into Python one line at a time, Python is treating them as an ordered sequence of statements with later statements able to retrieve data created in earlier statements. We are writing our first simple paragraph with four sentences in a logical and meaningful order. It is the nature of an interpreter to be able to have an interactive conversation as shown above. A compiler needs to be handed the entire program in a file, and then it runs a process to translate the high level source code into machine language and then the compiler puts the resulting machine language into a file for later execution.
If you have a Windows system, often these executable machine language programs have a suffix of “.exe” or “.dll” which stand for “executable” and “dynamically loadable library” respectively. In Linux and Macintosh there is no suffix that
uniquely marks a file as executable. It is not easy to read or write machine language so it is nice that we have interpreters
and compilers that allow us to write in a high-level language like Python or C.
Now at this point in our discussion of compilers and interpreters, you should be wondering a bit about the Python interpreter itself. What language is it written in? Is it written in a compiled language? When we type “python”, what exactly is happening? 
The Python interpreter is written in a high level language called “C”. You can look at the actual source code for the Python interpreter by going to www.python.org and working your way to their source code. So Python is a program itself and it is compiled into machine code and when you installed Python on your computer (or the vendor installed it), you copied a machine-code copy of the translated Python program onto your system. In Windows the executable machine code for Python itself is likely in a file with a name like:
C:\Python27\python.exe
That is more than you really need to know to be a Python programmer, but sometimes it pays to answer those little nagging questions right at the beginning.

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