IndentationError: two many levels of indentation

[Two Inches]

We've got this error when we tried to execute code that was created with 
a generator tool. The code had about 500 levels of indentation (nested 
if blocks). It is no problem for us to change the generator.

However, I couldn't find this limitation in the language reference. 
Shouldn't it be in there? What is the exact limit?

Is there any technical rational for this limit?