The Component Object Model (COM) is Microsoft’s newest integration technology and pervades Windows 95, 98, NT, and 2000. The DLL lets you call functions someone else has written; COM lets you talk to objects someone else has written. They don’t even have to be on the same computer!
Windows provides a host of API calls to get things done, but using the calls generally requires C programming expertise, and they have a tortuous syntax. COM provides alternative, easier-to-use interfaces to a wide range of operating-system services, and it lets applications expose and share their functionality as well. COM is now mature, stable, and as fast as using DLLs, but much easier to use, and so opens up many new possibilities. Want a spreadsheet and chart within your application? Borrow the ones in Excel. To a programmer with a COM-enabled language (and most of them are by now), Windows feels like a sea of objects, each with its own capabilities, standing by and waiting to help you get your job done.
Python’s support for COM is superb and is the thrust for a large portion of this book.