Re: recursive function: use a global or pass a parameter?

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From	Gregory Ewing <greg.ewing@canterbury.ac.nz>
Newsgroups	comp.lang.python
Subject	Re: recursive function: use a global or pass a parameter?
Date	Sun, 18 Jan 2015 10:25:42 +1300
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Yawar Amin wrote:

> Cool ... but it looks like this can still potentially hit the max
> recursion limit?

It depends on the nature of your data. If the data is
a tree, it's very unlikely you'll reach the recursion
limit unless the tree is massively unbalanced.

If there's a chance of that, or if the data structure
is really a graph that could contain long linear
chains, then a non-recursive solution is safer.

Incidentally, Python's pickle suffers from this
problem -- it's possible to create a structure that
can't be pickled due to excessive recursion depth:

 >>> x = []
 >>> for i in range(5000):
...  x = [x]
...
 >>> import pickle
 >>> s = pickle.dumps(x)
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
RuntimeError: maximum recursion depth exceeded while pickling an object

Fortunately, the kinds of structures that cause this
tend not to be used in Python, e.g. we normally use
Python list objects instead of linked lists. So most
of the time, pickle gets away with using recursion.

-- 
Greg

Thread

recursive function: use a global or pass a parameter? Tim <jtim.arnold@gmail.com> - 2015-01-16 09:49 -0800
  Re: recursive function: use a global or pass a parameter? Chris Angelico <rosuav@gmail.com> - 2015-01-17 04:56 +1100
    Re: recursive function: use a global or pass a parameter? Rustom Mody <rustompmody@gmail.com> - 2015-01-16 10:22 -0800
  Re: recursive function: use a global or pass a parameter? Peter Otten <__peter__@web.de> - 2015-01-16 19:34 +0100
    Re: recursive function: use a global or pass a parameter? Tim <jtim.arnold@gmail.com> - 2015-01-16 10:48 -0800
    Re: recursive function: use a global or pass a parameter? Yawar Amin <yawar.amin@gmail.com> - 2015-01-16 18:23 -0800
      Re: recursive function: use a global or pass a parameter? Yawar Amin <yawar.amin@gmail.com> - 2015-01-16 21:29 -0800
      Re: recursive function: use a global or pass a parameter? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-18 10:25 +1300
  Re: recursive function: use a global or pass a parameter? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-17 11:20 +1300
    Re: recursive function: use a global or pass a parameter? Chris Angelico <rosuav@gmail.com> - 2015-01-17 10:49 +1100
  Re: recursive function: use a global or pass a parameter? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-17 21:15 +1100
    Re: recursive function: use a global or pass a parameter? Roy Smith <roy@panix.com> - 2015-01-17 10:20 -0500
      Re: recursive function: use a global or pass a parameter? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-18 10:07 +1300
  Re: recursive function: use a global or pass a parameter? albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-01-17 17:30 +0000
    Re: recursive function: use a global or pass a parameter? Chris Angelico <rosuav@gmail.com> - 2015-01-18 06:27 +1100

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