I was reading about Cocoa framework
http://developer.apple.com/technology/cocoa.html "With the Cocoa Bridge, developers can create first-class Mac OS X applications using AppleScript, Ruby, and Python."
So, we can write Mac OS X applications with Python.
Is this true for writing iPhone applications?
No, only in Objective-C can you write iPhone apps.
Now there are some "converters" out there that can do some things like take some Java code and generate Objective-C from it, and there are even people that use Groovy scripts to generate Objective-C code.
You can always also write a web app that is "sized" for a mobile device, but I never use those apps myself.