Programming Python, Second Edition

Launching Programs on Windows

Suppose just for a moment, that you’ve been asked to write a big Python book, and want to provide a way for readers to easily start the book’s examples on just about any platform that Python runs on. Books are nice, but it’s awfully fun to be able to click on demos right away. That is, you want to write a general and portable launcher program in Python, for starting other Python programs. What to do?

In this chapter, we’ve seen how to portably spawn threads, but these are simply parallel functions, not external programs. We’ve also learned how to go about starting new, independently running programs, with both the fork/exec combination, and tools for launching shell commands such as os.popen. Along the way, though, I’ve also been careful to point out numerous times that the os.fork call doesn’t work on Windows today, and os.popen fails in Python release 1.5.2 and earlier when called from a GUI program on Windows; either of these constraints may be improved by the time you read this book (e.g., 2.0 improves os.popen on Windows), but they weren’t quite there yet as I wrote this chapter. Moreover, for reasons we’ll explore later, the os.popen call is prone to blocking (pausing) its caller in some scenarios.

Luckily, there are other ways to start programs in the Python standard library, albeit in platform-specific fashion:

• The os.spawnv and os.spawnve calls launch programs on Windows, much like a fork/exec call combination on Unix-like platforms.

• The ...