Import python files

There are many ways to import a python file, all with their pros and cons.

Don't just hastily pick the first import strategy that works for you or else you'll have to rewrite the codebase later on when you find it doesn't meet your needs.

I'll start out explaining the easiest example #1, then I'll move toward the most professional and robust example #5

Example 1, Import a python module with python interpreter:

1. Put this in /home/el/foo/fox.py:

   def what_does_the_fox_say():
     print("vixens cry")
   

2. Get into the python interpreter:

   el@apollo:/home/el/foo$ python
   Python 2.7.3 (default, Sep 26 2013, 20:03:06) 
   >>> import fox
   >>> fox.what_does_the_fox_say()
   vixens cry
   >>> 
   

   You imported fox through the python interpreter, invoked the python function what_does_the_fox_say() from within fox.py.

Example 2, Use execfile or (exec in Python 3) in a script to execute the other python file in place:

1. Put this in /home/el/foo2/mylib.py:

   def moobar():
     print("hi")
   

2. Put this in /home/el/foo2/main.py:

   execfile("/home/el/foo2/mylib.py")
   moobar()
   

3. run the file:

   el@apollo:/home/el/foo$ python main.py
   hi
   

   The function moobar was imported from mylib.py and made available in main.py

Example 3, Use from ... import ... functionality:

1. Put this in /home/el/foo3/chekov.py:

   def question():
     print "where are the nuclear wessels?"
   

2. Put this in /home/el/foo3/main.py:

   from chekov import question
   question()
   

3. Run it like this:

   el@apollo:/home/el/foo3$ python main.py 
   where are the nuclear wessels?
   

   If you defined other functions in chekov.py, they would not be available unless you import *

Example 4, Import riaa.py if it's in a different file location from where it is imported

1. Put this in /home/el/foo4/stuff/riaa.py:

   def watchout():
     print "my message"
   

2. Put this in /home/el/foo4/main.py:

   import sys 
   import os
   sys.path.append(os.path.abspath("/home/el/foo4/stuff"))
   from riaa import *
   
   watchout()
   

3. Run it:

   el@apollo:/home/el/foo4$ python main.py 
   my message
   

   That imports everything in the foreign file from a different directory.

Example 5, Import files in python with the bare import command:

1. Make a new directory /home/el/foo5/

2. Make a new directory /home/el/foo5/herp

3. Make an empty file named __init__.py under herp:

   el@apollo:/home/el/foo5/herp$ touch __init__.py
   el@apollo:/home/el/foo5/herp$ ls
   __init__.py
   

4. Make a new directory /home/el/foo5/herp/derp

5. Under derp, make another __init__.py file:

   el@apollo:/home/el/foo5/herp/derp$ touch __init__.py
   el@apollo:/home/el/foo5/herp/derp$ ls
   __init__.py
   

6. Under /home/el/foo5/herp/derp make a new file called yolo.py Put this in there:

   def skycake():
     print "SkyCake evolves to stay just beyond the cognitive reach of " +
     "the bulk of men. SKYCAKE!!"
   

7. The moment of truth, Make the new file /home/el/foo5/main.py, put this in there;

   from herp.derp.yolo import skycake
   skycake()
   

8. Run it:

   el@apollo:/home/el/foo5$ python main.py
   SkyCake evolves to stay just beyond the cognitive reach of the bulk 
   of men. SKYCAKE!!
   

   The empty __init__.py file communicates to the python interpreter that the developer intends this directory to be an importable package.

If you want to see my post on how to include ALL .py files under a directory see here: http://stackoverflow.com/a/20753073/445131

Example 6, use os.system("python yourfile.py")

import os
os.system("python yourfile.py")

Bonus protip

whether you are using Mac, Linux or Windows, you need to be using python's idle editor as described here. It will unlock your python world. http://www.youtube.com/watch?v=DkW5CSZ_VII

http://stackoverflow.com/a/20749411/188963