"Marc 'BlackJack' Rintsch" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
| f([1, 2, 3])
| r1 f([2, 3]) + [1]
| r2 f([3]) + [2] + [1]
| r3 f([]) + [3] + [2] + [1]
| r4 [] + [3] + [2] + [1]
I might help to note that the above is effectively parenthesized
( ( ([]+{3]) + [2]) +[1])
*and* that each addition (in each pair of parentheses) is done
in a different execution frame (see below).
| And now the calls return:
|
| r3 [3] + [2] + [1]
| r2 [3, 2] + [1]
| r1 [3, 2, 1]
| > [3, 2, 1] # how this come here? how python save variables from each
| > recursion?
*Each time* a function is called, an execution frame is created(1) that is
separate from the function object itself. Each execution frame has its own
set of local variables. In particular, each has its own slices of the
original list.
There have been languages, for instance, Fortran IV, where local variables
were part of the function 'object' and which therefore prohibited recursion
because of the very problem you alluded to in your question. (My guess is
the functions had an InUse flag that was checked when the function was
called.)
tjr
(1) A minor variation would be for function objects to have one
pre-allocated execution frame for non-recursive calls and others allocated
as needed for recursive calls.
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