What does GCC have to do with a python interpreter?

Question

I just noticed this on my macintosh. Running $ python fires up an interpreter session with the following lines:

$ python2.7
Python 2.7.10 (default, Feb  6 2017, 23:53:20) 
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.34)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 

The second line of the starting up text mentions GCC and clang versions.

How are these two related to the python interpreter? Given that python is an interpreted language, there should be no whisper of a compiler at all, so I was curious as to why this is shown.

Now here's the same thing with python3.6:

$ python3.6
Python 3.6.0 (v3.6.0:41df79263a11, Dec 22 2016, 17:23:13) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 

This time there's no mention of clang. Why's that?

Answer 1

The CPython interpreter is itself written in C. It matters what compiler was used to convert the C code into a binary executable; behaviour and performance can differ in subtle ways, so it is mentioned in the banner.

You have two different Python binaries, the differences in the banner reflect differences in how those binaries where built. Since the Python 2.7 release is the one that comes bundled with OS X, it was built by Apple engineers using a different toolchain (using the clang compiler) from the Python 3.6 installation, which you must have installed separately (OS X doesn't include Python 3.6 yet). The latter was compiled with the GCC compiler.