On 9/25/2013 7:24 PM, Arturo B wrote:
Hi, I'm doing Python exercises and I need to write a function to flat nested lists as this one:[[1,2,3],4,5,[6,[7,8]]] To the result: [1,2,3,4,5,6,7,8] So I searched for example code and I found this one that uses recursion (that I don't understand): def flatten(l): ret = [] for i in l: if isinstance(i, list) or isinstance(i, tuple): ret.extend(flatten(i)) #How is flatten(i) evaluated? else: ret.append(i) return ret So I know what recursion is, but I don't know how is flatten(i) evaluated, what value does it returns?
It is not clear what part of 'how' you do not understand this. Perhaps that fact that a new execution frame with a new set of locals is created for each call. So calling flatten from flatten is no different than call flatten from anywhere else.
If a language creates just one execution frame for the function, attached to the function (as with original Fortran, for instance), then recursion is not allowed as a 2nd call would interfere with the use of the locals by the 1st call, etc.
-- Terry Jan Reedy -- https://mail.python.org/mailman/listinfo/python-list
