This script recursively searches for python.exe in the C partition of the system and adds its path to the system's PATH environment variable to help new users.

PyWinPath.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
#  PyWinPath.py  
#
#  Copyright 2015 Ericson Willians (Rederick Deathwill) <EricsonWRP@ERICSONWRP-PC>
#  
#  This script recursively searches for python.exe in the C partition of the system,
#  And adds its path to the system's PATH environment variable to help new users.
#  It also considers some basic common softwares that uses Python, such as GIMP, and ignores them.
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#  
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#  
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
#  MA 02110-1301, USA.
#  

import os, sys
from subprocess import check_call
if sys.hexversion > 0x03000000:
    import winreg
else:
    import _winreg as winreg

class Win32Environment:
	
    """
    Brilliant Utility class to get/set windows environment variables using winreg.
    Got from: http://code.activestate.com/recipes/577621/
    """

    def __init__(self, scope):
        assert scope in ('user', 'system')
        self.scope = scope
        if scope == 'user':
            self.root = winreg.HKEY_CURRENT_USER
            self.subkey = 'Environment'
        else:
            self.root = winreg.HKEY_LOCAL_MACHINE
            self.subkey = r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'

    def getenv(self, name):
        key = winreg.OpenKey(self.root, self.subkey, 0, winreg.KEY_READ)
        try:
            value, _ = winreg.QueryValueEx(key, name)
        except WindowsError:
            value = ''
        return value

    def setenv(self, name, value):
        # Note: for 'system' scope, you must run this as Administrator
        key = winreg.OpenKey(self.root, self.subkey, 0, winreg.KEY_ALL_ACCESS)
        winreg.SetValueEx(key, name, 0, winreg.REG_EXPAND_SZ, value)
        winreg.CloseKey(key)
        # For some strange reason, calling SendMessage from the current process
        # doesn't propagate environment changes at all.
        # TODO: handle CalledProcessError (for assert)
        check_call('''\
"%s" -c "import win32api, win32con; assert win32api.SendMessage(win32con.HWND_BROADCAST, win32con.WM_SETTINGCHANGE, 0, 'Environment')"''' % sys.executable)

if __name__ == "__main__":
	
	win = Win32Environment('system')
	PATH = os.environ["PATH"].split(';')
	search_for = "python.exe"
	list_of_python_software = ["eclipse", "gimp", "blender", "pycharm", "mysql"]
	if "python" and "anaconda" not in os.environ["PATH"].lower():
		for root, dirs, files in os.walk("C:\\"):
			try:
				print("Searching for python.exe in " + root)
				if search_for in files and not [True for software in list_of_python_software if software in root.lower()][0]:
					pass
			except Exception as e:
				if isinstance(e, UnicodeEncodeError):
					pass
				elif isinstance(e, IndexError):
					print("Found at " + os.path.join(root, search_for))
					PATH.append(root)
					win.setenv("PATH", ';'.join(PATH) + ';')
					print("The path was properly added to the system's PATH environment variable.")
					print("Now, just type 'python' in cmd and have fun.")
					break
	else:
		print("You already have python in your system's PATH environment variable.")

Em vez de

            except Exception as e:
                if isinstance(e, UnicodeEncodeError):
                    pass
                elif isinstance(e, IndexError):
                    print("Found at " + os.path.join(root, search_for))
                    PATH.append(root)
                    win.setenv("PATH", ';'.join(PATH) + ';')
                    print("The path was properly added to the system's PATH environment variable.")
                    print("Now, just type 'python' in cmd and have fun.")
                    break

Que tal:

            except IndexError as e:
                print("Found at " + os.path.join(root, search_for))
                PATH.append(root)
                win.setenv("PATH", ';'.join(PATH) + ';')
                print("The path was properly added to the system's PATH environment variable.")
                print("Now, just type 'python' in cmd and have fun.")
                break
            except UnicodeEncodeError:
                pass

Fica mais claro dessa forma.