edit path variable using python

>>> import sys
>>> print(sys.executable)
C:\path\to\python.exe

To add Python to the Windows Path, follow these steps:

1. Start the Run box and enter sysdm.cpl
2. In the System Properties window go to the Advanced tab and 
   click the Environment Variables button
3. In the System variable window, find the Path variable and 
   click Edit
4. Position your cursor at the end of the Variable value line 
   and add the path to the python.exe file, preceeded with 
   the semicolon character (;)

app_path = os.path.join(root_path, 'other', 'dir', 'to', 'app')
os.environ["PATH"] += os.pathsep + app_path