inner methods and recursion
gagsl-py2 at yahoo.com.ar
Tue Jan 19 03:07:11 CET 2010
En Mon, 18 Jan 2010 19:00:17 -0300, Steve Howell <showell30 at yahoo.com>
> Hi, I have a style/design question relating to recursion and inner
> I wrote some code recently that implements a recursive algorithm that
> takes several parameters from the original caller. Once the algorithm
> starts running and recursing, those parameters remain the same, so I
> define an inner method called "recurse" that essentially curries those
> parameters. In particular, the recurse method can get passed to a
> callback method that the caller supplies, so that the caller can wrap
> the recursive step with their own logic.
Python already have lexical scoping, you can take advantage of it. On any
non-prehistoric version of Python you may write:
output = 
# ... the real work ...
# recursive call:
output += branch_method(prefix, block, _indent_lines)
The real work happens inside _indent_lines, and it has access to the outer
indent_lines scope, where all remaining parameters are defined.
> The only thing I don't like about the technique that I'm using is that
> it seems needlessly repetitive to define mostly the same parameter
> list in two different places. The repetition seems mostly harmless,
> but it seems like some kind of a smell that I'm overlooking a simpler
> way to write the code. I just can't put my finger on what it is.
Is the above technique what you were looking for?
> Does anybody have any inspiration here? I vaguely recall a discussion
> some time back about having some kind of @recursive decorator, but I
> can't seem to find the thread.
The thread I remember was about making "true" recursive calls (normal
recursive calls at global or method scope are not truly recursive: they
actually perform a name lookup, which may or may not yield the original
function). In the above case, that doesn't happen, the recursive call
resolves the _indent_lines name directly using a cell "pointing" into its
container local scope.
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