Is there a way to make a recursion method with unlimited depth in Python?

Question

For example, when writing some algorithms on graphs like

def f(graph):
    #graph is dictionary of pairs vertex_i:{set of edges (i,j)} for 1<=i,j<=n
    def g(vertex):
        for vertex1 in graph:
            do sth
            ...
            for (i,j) in graph[vertex1]:
                ...
                g(j)#recursive call
        ...
        return ...

    return g(1)

limited depth of recursion is sometimes very annoying, because code becomes much longer and more complicated if you have to avoid recursion. Is there a way to reach unlimited depth? Maybe you can describe your general solution of the problem on the following method

def nthNumber(n):
    if n==1: return 1
    else: return nthNumber(n-1)+1

(I know it's simple stupid and please don't give answers like "You should have written just nthNumber(n): return n " - I'm intrested in general solution). Thanks for help!

Let me put in another way: is it possibly to make a recurison method with max. depth 104 or 105? — Antoine
– Antoine, Commented Apr 20, 2013 at 20:47
You can set the recursion limit to 10**4, but you may end up crashing python (it is probably over the safe limit - which is OS dependent). Also : stackoverflow.com/questions/2917210/… — root
– root, Commented Apr 20, 2013 at 20:52

Martijn Pieters · Accepted Answer · 2013-04-20 20:45:25Z

7

Unlimited recursion would require infinite resources; every function call requires a stack entry, and there is only a finite amount of memory to hold those. So, no, you cannot have unlimited recursion depth.

You can raise the limit, by calling sys.setrecursionlimit().

answered Apr 20, 2013 at 20:45

Martijn Pieters

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2 Comments

nehem Over a year ago

Unlimited != Infinite, What he was asking for is un'limited', meaning Python wouldn't enforce any limits on this.

Martijn Pieters Over a year ago

@itsneo: that's just... splitting hairs. You can raise the limit to beyond what the OS or available hardware would allow. The point is that you'll run into a limit.

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