Nested loop limit?

Michael Hudson mwh at python.net
Fri Jul 9 15:49:17 CEST 2004


Peter Hansen <peter at engcorp.com> writes:

> Nelson Minar wrote:
> 
> > Why does CPython have a limit of 21 nested blocks?
> > I'm never going to write code this deeply nested by hand, but I
> > could
> > imagine writing a program that does. It's also sort of a weird limit.
> 
> Is the fact that the limit is actually 20 less weird?  (The 21 was
> where "n" was after it raised an exception, not the last legal
> amount of indentation.)
> 
> And I think the answer is probably something like "CPython,
> being written in C, tends to have certain hard-coded limits
> much like C programs always do, rather than being nice and
> flexible like programs written with more sophisticated languages
> like, say, Python."  :-)

Spot on.  This has to do with the 'blockstack', very much an internal
detail to Python's implementation.  We'd like to get rid of it (*not*
because we want to let people write code with more than 20 nested for
loops :-) but it's not especially easy (finally: blocks are the
biggest problem).

Cheers,
mwh

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