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Loop Statements Versus Recursion

Though recursion works for summing in the prior sections’ examples, it’s probably overkill in this context. In fact, recursion is not used nearly as often in Python as in more esoteric languages like Prolog or Lisp, because Python emphasizes simpler procedural statements like loops, which are usually more natural. The while, for example, often makes things a bit more concrete, and it doesn’t require that a function be defined to allow recursive calls:

>>> L = [1, 2, 3, 4, 5]
>>> sum = 0
>>> while L:
...     sum += L[0]
...     L = L[1:]
...
>>> sum
15

Better yet, for loops iterate for us automatically, making recursion largely extraneous in most cases (and, in all likelihood, less efficient in terms of memory space and execution time):

>>> L = [1, 2, 3, 4, 5]
>>> sum = 0
>>> for x in L: sum += x
...
>>> sum
15

With looping statements, we don’t require a fresh copy of a local scope on the call stack for each iteration, and we avoid the speed costs associated with function calls in general. (Stay tuned for Chapter 20’s timer case study for ways to compare the execution times of alternatives like these.)