Calling 'python' via subprocess.call ignoring passed %PATH% #68981

Activity

1. phbarnacle commented on Aug 5, 2015

   

   phbarnaclemannequin

   on Aug 5, 2015

   MannequinAuthor

   More actions

   I just noticed that there is a litte inconvenience when I try to invoke 'python' via subprocess.call passing an environment (%PATH%) from a script. I pass an environment where %PATH% only contains one directory where a python2.7.3-exe is present (I checked with "subprocess.call(['where','python'],env=environment)" that python is found there). However when calling "subprocess.call(['python'],env=environment)" python 2.7.9 is opened, which is the python version I called the script with. Seems inconvenient to me.

   Greetings
2. phbarnacle

   added

   OS-windows

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Aug 5, 2015
3. pfmoore commented on Aug 5, 2015

   

   pfmoore

   on Aug 5, 2015

   Member

   More actions

   This is standard Windows behaviour. Executables are always located first in the directory where your program (in this case the Python executable) is running from - even before searching PATH.

   If you want to use a different Python, you should specify the full path to the executable - "subprocess.call(["C:\\Python34\\python.exe"])".
4. pfmoore

   closed this as completedon Aug 5, 2015
5. pfmoore

   added

   invalid

   on Aug 5, 2015
6. eryksun commented on Aug 5, 2015

   

   eryksun

   on Aug 5, 2015

   Contributor

   More actions

   Popen calls Windows CreateProcess. If the Popen "executable" argument isn't used or if the file from the command line doesn't include a directory path, then CreateProcess searches for it in the following directories:

   1. The directory from which the application loaded.
   2. The current directory for the parent process.
      * This step is skipped if the parent defines
        %NoDefaultCurrentDirectoryInExePath%.
   3. The 32-bit Windows system directory.
   4. The 16-bit Windows system directory. 
   5. The Windows directory. 
   6. The directories that are listed in the PATH 
      environment variable. 
   

   Also note that the PATH searched is that of the *parent* process; the "env" parameter doesn't affect this.

   Call the SearchPath function if you need a custom search for the fully qualified path.

       import ctypes
       from ctypes import wintypes
   
       kernel32 = ctypes.WinDLL('kernel32')
   
       kernel32.SearchPathW.argtypes = (
           wintypes.LPCWSTR,                   # _In_opt_  lpPath
           wintypes.LPCWSTR,                   # _In_      lpFileName
           wintypes.LPCWSTR,                   # _In_opt_  lpExtension
           wintypes.DWORD,                     # _In_      nBufferLength
           wintypes.LPWSTR,                    # _Out_     lpBuffer
           ctypes.POINTER(wintypes.LPWSTR))    # _Out_opt_ lpFilePart
                                               
       def search_path(filename, path=None, ext='.exe'):
           length, new_length = 0, 260
           while new_length > length:
               length = new_length
               filepath = (ctypes.c_wchar * length)()
               new_length = kernel32.SearchPathW(path, filename, ext,
                                                 length, filepath, None)
           return filepath.value

   For example:

       >>> search_path('python')
       u'C:\\Program Files\\Python27\\python.exe'
       >>> import os            
       >>> search_path('python', os.environ['PATH'])
       u''
   
       >>> search_path('more.com', os.environ['PATH'])
       u'C:\\Windows\\System32\\more.com'
       >>> search_path('more', ext='.com')            
       u'C:\\Windows\\system32\\more.com'
7. ezio-melotti

   transferred this issue fromon Apr 10, 2022