Popen with conflicting executable/path

by

Search for a program is not trivial. I’d specify the full path to the convert.exe executable explicitly instead.

subprocess uses CreateProcess on Windows that looks in system32 directory even before any other directory in %PATH%:

… If the file name does not contain an extension, .exe is appended.
Therefore, if the file name extension is .com, this parameter must
include the .com extension. If the file name ends in a period (.) with
no extension, or if the file name contains a path, .exe is not
appended. If the file name does not contain a directory path, the
system searches for the executable file in the following sequence:

  1. The directory from which the application loaded.
  2. The current directory for the parent process.
  3. The 32-bit Windows system directory. Use the GetSystemDirectory function to get the path of this directory.
  4. The 16-bit Windows system directory. There is no function that obtains the path of this directory, but it is searched. The name of this directory is System.
  5. The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
  6. The directories that are listed in the PATH environment variable. Note that this function does not search the per-application path specified by the App Paths registry key. To include this per-application path in the search sequence, use the ShellExecute function.

Therefore convert is equivalent to convert.exe in this case. It first looks in a directory that contains sys.executable e.g., C:\Python27. Then in the current directory: where you started the Python script from. Then in system32 where it finds convert.exe (filesystem utility, not imagemagick).

You could try to remove system32 directory from os.environ['PATH'] it may(?) suppress checking it: Popen(cmd, env=no_system32_environ) but it is fragile (worse than the explicit path).

There is a related issue on Python bug tracker: “Subprocess picks the wrong executable on Windows.”

cmd.exe (the shell) uses different algorithm. See How does Windows locate files input in the shell?

If you set shell=True then the search sequence for convert program:

  1. convert is not an internal shell command
  2. there is no explicit path, so the search continues
  3. search the current directory
  4. search each directory specified by the PATH environment variable, in the order listed

%PATHEXT% defines which file extensions are checked and in what order e.g., convert.com, convert.exe, convert.bat, convert.cmd if %PATHEXT% is .com;.exe;.bat;.cmd.

More Related Contents:

  1. Popen waiting for child process even when the immediate child has terminated
  2. How do I get all of the output from my .exe using subprocess and Popen?
  3. How do I eliminate Windows consoles from spawned processes in Python (2.7)? [duplicate]
  4. Python subprocess/Popen with a modified environment
  5. Intercepting stdout of a subprocess while it is running
  6. Python: how to kill child process(es) when parent dies?
  7. subprocess: deleting child processes in Windows
  8. How do I get ‘real-time’ information back from a subprocess.Popen in python (2.5)
  9. subprocess.Popen() error (No such file or directory) when calling command with arguments as a string
  10. Using subprocess to run Python script on Windows
  11. How to write to stdout AND to log file simultaneously with Popen?
  12. link several Popen commands with pipes
  13. Python running as Windows Service: OSError: [WinError 6] The handle is invalid
  14. Python subprocess and user interaction
  15. Keep a subprocess alive and keep giving it commands? Python
  16. Launch a shell command with in a python script, wait for the termination and return to the script
  17. How to run a background process and do *not* wait?
  18. Run process as admin with subprocess.run in python
  19. real time subprocess.Popen via stdout and PIPE
  20. ‘^’ is ignored by Python – how to escape ‘^’ character in Popen Windows?
  21. What’s the difference between subprocess Popen and call (how can I use them)?
  22. python subprocess Popen environment PATH?
  23. Why does subprocess.Popen() with shell=True work differently on Linux vs Windows?
  24. Launch IPython notebook with selected browser
  25. Sending ^C to Python subprocess objects on Windows
  26. Execute Commands Sequentially in Python?
  27. How to do multiple arguments with Python Popen?
  28. subprocess.wait() not waiting for Popen process to finish (when using threads)?
  29. Opening a process with Popen and getting the PID
  30. What is the subprocess.Popen max length of the args parameter?

Leave a Comment