this recursive definition of sum thrumped me, is this some sort of
gotcha or am I just braindead today?
and yes i know this is easy a a for x in xs acc += x or just using the
builtin.
def suma(xs, acc=0):
if len(xs) == 0:
acc
else:
suma(xs[1:], acc+xs[0])
it returns none.
def summa(xs):
if not xs:
0
else:
xs[0]+summa(xs[1:])
Traceback (most recent call last):
File "<pyshell#6>", line 1, in <module>
summa([1,2,3,4,5])
File "<pyshell#5>", line 5, in summa
xs[0]+summa(xs[1:])
File "<pyshell#5>", line 5, in summa
xs[0]+summa(xs[1:])
File "<pyshell#5>", line 5, in summa
xs[0]+summa(xs[1:])
File "<pyshell#5>", line 5, in summa
xs[0]+summa(xs[1:])
File "<pyshell#5>", line 5, in summa
xs[0]+summa(xs[1:])
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'
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