add %mrun and %addpath magics that searches pythonpath and allows adding custom paths to an %run like command (%mrun)

01-run-paths.py

# based on ipython issue #101
#
# author: Gaute Hope <gaute.hope@nersc.no> / 2015
#
# references:
#
#   https://github.com/ipython/ipython/issues/101
#   http://ipython.org/ipython-doc/dev/config/custommagics.html
#

import os
import sys

from IPython.utils.path import filefind

_custom_paths = []

def find_in_pythonpath (filename):
  global _custom_paths

  try:
    path_dirs = ['.'] + _custom_paths + os.environ['PYTHONPATH'].split(':')
  except:
    path_dirs = ['.'] + _custom_paths

  return filefind(filename, path_dirs)

def find_in_syspath(filename):
  return filefind(filename, sys.path)

from IPython.core.magic import line_magic, Magics, magics_class, register_line_magic

@register_line_magic
def mrun (line):
  ip = get_ipython()
  ip.magics_manager.magics['line']['run'](line, file_finder=find_in_pythonpath)

del mrun

@register_line_magic
def addpath (line):
  global _custom_paths
  _custom_paths.append(line)

del addpath

This is what I was looking for, thanks a lot!
I have taken your code and done some small modifications, you could see it in https://gist.github.com/dgerod/549273a7bf5114d008b6