+1 for a more informative repr (like we did with regex match objects).

There are a lot of parameters to subprocess.Popen().  RR is on the right track suggesting that only a small, useful subset of those be included:  args and the return code.  

We could add the *pid* argument as well, but may be no more useful or attractive than the current repr's object id.

The repr should be enclosed in angle brackets because it can't recreate the object.