Q:

How to execute a file within the python interpreter?

I'm trying to execute a file with python commands from within the interpreter. 
EDIT: I'm trying to use variables and settings from that file, not to invoke a separate process.

A:

For Python 2:
>>> execfile('filename.py')

For Python 3:
>>> exec(open("filename.py").read())
# or
>>> from pathlib import Path
>>> exec(Path("filename.py").read_text())

See the documentation. If you are using Python 3.0, see this question.
See answer by @S.Lott for an example of how you access globals from filename.py after executing it.

A:

Several ways.
From the shell
python someFile.py

From inside IDLE, hit F5.
If you're typing interactively, try this: (Python 2 only!)
>>> variables= {}
>>> execfile( "someFile.py", variables )
>>> print variables # globals from the someFile module

For Python3, use:  
>>> exec(open("filename.py").read())

A:

Python 2 + Python 3
exec(open("./path/to/script.py").read(), globals())

This will execute a script and put all it's global variables in the interpreter's global scope (the normal behavior in most scripting environments).
Python 3 exec Documentation

