I know Objective-C is the recommended language for mac app store apps. What if I would like to write a mac app with python? Will my app be rejected when published?
The App Store will accept any binary as long as it doesn't require anything that isn't included with the system or in the binary. Because Mac OS X includes Python, it should be acceptable. There are a variety of libraries and helpful tools for writing Mac apps in Python such as Py2app and PyObjC. Some developers have successfully used them to write apps and get them on the app store.
Relevant guidelines from Apple: