Open a file from Blender using python

Coding Beginning Blender Code and Development
1

I would like to do a very simple thing but I am quite lost.
I want to write a script in python which open a .blend file but using the blender.app which is located in the same folder with the blend file, not with the blender.app which is located in Applications. (using Macosx)

So I was thinking that this should do the job…but instead it opens blender twice…

import os

path = os.getcwd()
print(path)
os.system("cd path/")
os.system("open blender.app Import_mhx.blend")

I also tried this one

import os

path = os.getcwd()
print(path)
os.system("cd path/")
os.system("open Import_mhx.blend")

but unfortunately it opens the .blend file with the default blender.app which is located in Applications…

any idea would be really appreciated:)

2 

import os
import subprocess

path = os.getcwd()
print(path)
os.system("cd path/")

subprocess.check_call(["open", "-a", os.path.join(path, "blender.app"),
                       "Import_mhx.blend"])